MYSQL TECHNICAL REFERENCE MANUAL. - INTRODUCTION P 5 GENERAL INFORMATION ABOUT MYSQL P 6

MYSQL TECHNICAL REFERENCE MANUAL. - INTRODUCTION P 5 GENERAL INFORMATION ABOUT MYSQL P 6

MySQL Technical Reference Manual. Introduction [p 5] General Information about MySQL [p 6] What is MySQL? [p 6] History of MySQL [p 6] The main features in MySQL [p 6] What is the current MySQL version? [p 7] How do I get MySQL? [p 7] Should I get MySQL in source or binary distribution? [p 8] Which operating systems does MySQL support? [p 8] What languages are supported by MySQL. [p 8] How/when will you release updates? [p 9] What is UNIREG ? [p 9] General SQL information and tutorials [p 10] What are stored procedurs and triggers and so on [p 10] MySQL mailing lists and how to ask questions [p 11] Subscribing to/un-subscribing from the MySQL mailing list.

[p 11] Asking questions or reporting bugs. [p 11] Guidelines for answering questions on the mailing list. [p 12] When do I have/want to pay for MySQL? [p 13] How much does MySQL cost? [p 13] How do I get comercial support [p 14] Types of comercial support [p 14] How do I pay for a license? [p 15] Who do I contact when I want support/a license? [p 15] What Copyright does MySQL use? [p 16] When may I distribute MySQL commercially without a fee [p 16] I’m selling a product that can be configured to use MySQL [p 17] I am running a commercial web server using MySQL. [p 17] Do I need a license to sell commercial perl/tcl/PHP etc applications? [p 17] Possible future changes in the licensing.

[p 18] How standards compatible are MySQL [p 19] What extension has MySQL to ANSI SQL92? [p 19] What functionality is missing in MySQL. [p 20] What standards does MySQL follow? [p 21] What functions exist only for compatibility? [p 21] Limitations of BLOB and TEXT types [p 21] How to go cope without COMMIT-ROLLBACK [p 21] Compiling and installing MySQL [p 24] Compiling MySQL [p 24] Problems starting MySQL [p 24] Automatic start/stop of MySQL [p 25] How to debug MySQL [p 25] How does MySQL privileges work [p 26] How does the privilege system work? [p 26] 1

Adding new user privileges to MySQL [p 28] Default privileges. [p 28] A example of permission setup. [p 29] MySQL language reference [p 30] Literals. How do you write strings and numbers? [p 30] Column types. [p 31] More about data types [p 33] Database size info. [p 33] The numeric types [p 33] TIMESTAMP type [p 33] TEXT and BLOB types [p 33] ENUM type [p 34] SET type [p 34] Column indexes [p 35] Multiple field indexes [p 35] Type mapping (to ease moving tabel definitions between different databases engines) [p 35] CREATE TABLE syntax. [p 36] ALTER TABLE syntax [p 37] DROP TABLE syntax. [p 38] DELETE syntax.

[p 38] SELECT syntax [p 39] Functions [p 40] INSERT syntax [p 45] LOAD DATA INFILE syntax [p 45] UPDATE syntax [p 47] SHOW syntax. Get information about names of columns. [p 47] EXPLAIN syntax. Get information about a SELECT. [p 47] DESCRIBE syntax. Get information about columns. [p 48] Lock tables syntax [p 48] SET OPTION syntax. [p 48] GRANT syntax. (Compatibility function). [p 49] CREATE INDEX syntax (Compatibility function). [p 49] DROP INDEX syntax (Compatibility function). [p 49] Is MySQL picky about reserved words? [p 49] How safe/stable is MySQL [p 52] How stable is MySQL? [p 52] Why are there is so many release of MySQL? Is it because there are so many bugs? [p 54] Checking a table for errors.

[p 54] How to repair tables. [p 55] Is there anything special to do when upgrading/downgrading MySQL? [p 56] How to get maximum performance out of MySQL [p 57] How does MySQL use memory ? [p 57] How does MySQL use keys? [p 58] How does MySQL open & close tables? [p 59] How should I arrange my table to be as fast/small as possible? [p 59] What affects the speed of the INSERT statement? [p 60] 2

What affects the speed of DELETE statement? [p 60] What kind of optimisation is done on the WHERE clause? [p 60] How can I change the buffer sizes of mysqld ? [p 61] What options to use to get MySQL to run at full speed? [p 62] How to get MySQL to run as fast as possible with little memory? [p 62] What are the different row formats? Or when to use VARCHAR/CHAR? [p 63] Why so many open tables? [p 64] MySQL Utilites [p 65] Overview of the different MySQL programs [p 65] The MySQL table check, optimize and repair program [p 66] Getting low level table information [p 66] The MySQL compressed read only table generator [p 70] Adding functions to MySQL [p 75] Adding new functions to MySQL [p 75] ODBC [p 76] Which operating systems does MySQL ODBC support? [p 76] How should I report problems with MySQL ODBC? [p 76] Programs known to work with MyODBC.

[p 76] How do I fill in the various fields in the ODBC administrator program? [p 76] Problems [p 78] Why do I get ’Access denied’? [p 78] How to run MySQL as a normal user. [p 79] Problems with file permissions [p 79] Problems using DATE fields. [p 80] MySQL client tools and API’s [p 81] MySQL C API [p 81] Why is it that after mysql_query() returns success, mysql_store_result() sometimes returns NULL? [p 82] What results can I get from a query? [p 83] How can I get the unique ID for the last row? [p 83] What is the difference between mysql_use_result() and mysql_store_result() modes? [p 83] Problems linking with C API.

[p 84] How to make a threadsafe client [p 84] Making a threadsafe client [p 84] What is the difference between different thread packages? [p 85] MySQL Perl API’s [p 85] mysqlperl [p 85] DBD::mysql [p 85] MySQL JAVA connectivity (JDBC) [p 85] MySQL C++ API’s [p 85] MySQL TCL API’s [p 85] MySQL Python API’s [p 86] MySQL Python API’s [p 86] How does MySQL compare with other databases [p 87] How does MySQL compare with mSQL [p 87] How about mSQL tools like msql-tcl, msqljava? [p 88] 3

How different from mSQL are the MySQL client/server communications protocols? [p 88] What are the differences in the SQL syntax between MySQL & mSQL 2.0? [p 89] Problems with AND and OR priority [p 91] This document was generated on 3 November 1997 using the texi2html translator version 1.51 (extended by davida@detron.se). 4

Go to the first, previous, next [p 6] , last [p 87] section, table of contents [p 1] . Introduction This is the technical manual about MySQL. This version is about the 3.21.x version of MySQL. This document contains the basic documenatation about MySQL.

The latest version of this manual can be found at http://www.tcx.se/ This manual is currently available in TeXInfo, Raw text, Info, Postscript and HTML versions. The primary document is the TeXInfo file. The HTML version is automatically produced with texi2html. The ASCII and info version is produced using makeinfo. The Postscript version is produced using texi2dvi and divps.

If you have any suggestions concerning additions or corrections, please send them to the MySQL mailing list mysql@tcx.se withthe following subject line; documentation suggestion: [Insert Topic Here]. See section Subscribing to/un-subscribing from the MySQL mailing list. [p 11] . This manual is written and maintained by David Axmark, Michael (Monty) Widenius and Kim Aldale. Go to the first, previous, next [p 6] , last [p 87] section, table of contents [p 1] . 5

Go to the first [p 5] , previous [p 5] , next [p 11] , last [p 87] section, table of contents [p 1] .

General Information about MySQL What is MySQL? MySQL is a SQL (Structured Query Language) database server. SQL is the most popular database language in the world. MySQL is a client server implementation that consists of a server daemon mysqld and many different client programs/libraries. The main goals of MySQL are speed and robustness. The base upon which MySQL is built is a set of routines that have been used in a highly demanding production environment for many years. While MySQL is currently still in development it already offers a rich and highly useful function set.

See the ‘CREDITS’ file in the distribution for persons that have been involved in the MySQL project. History of MySQL We once started off with the intension to use mSQL to connect to our own fast low level (ISAM) tables. However, after some testing we came to the conclusion that mSQL was not fast or flexible enough for our needs. This resulted in a new SQL interface to our database but with almost the same API interface as mSQL. This API was chosen to ease porting of third party code. It is not perfectly clear where the name MySQL derives from. Our base directory and a large amount of our libraries and tools have had the prefix ’my’ for well over 10 years.

However, Monty’s daughter (some years younger) is also named My. So which of the two gave its name to MySQL is still a mystery, even for us.

The main features in MySQL Multi-threaded. C, C++, JAVA, Perl, Python and TCL API’s. See section MySQL client tools and API’s [p 81] Lots of column types like: signed/unsigned integers 1,2,3,4,8 bytes long, FLOAT, CHAR, VARCHAR, TEXT, BLOB, DATE, SET and ENUM types. See section Column types. [p 31] Join optimiser with one-sweep multi-join (all joins made in one pass). Full function support in the SELECT and WHERE parts. Example: select column1+column2 from table where column1/column2 > 0 SQL functions are implemented through a very optimised class library and should be as fast as they can get! Usually there shouldn’t be any memory allocation at all after the query initialisation.

Full support for SQL GROUP BY and ORDER BY. Support for group functions (SUM, MAX and MIN). A privilege and password system with is very flexible and secure. Allows host based verification. All password traffic on the net is encrypted. 6

Very fast B-tree disk tables with key compression. Fixed and variable length records. 16 indexes/table. Each index may consist of 1 to 15 columns/parts of columns. Max key length is 127 bytes. A key may be a prefix of a CHAR field. ODBC Open-DataBase-Connectivity for Windows95 (with source). All ODBC 2.5 functions and lots of others.

In memory hash tables always used as temporary tables. Can handle big databases (we are using MySQL with some databases that contain 50,000,000 records). All columns have default values. One can always use INSERT on any subset of columns. Uses GNU autoconf for portability.

Written in C and C++. Tested with gcc 2.7.2. A thread based memory allocation system (very fast and no memory trashing). No memory leaks. Tested with a commercial memory leakage detector (purify). A very fast table check and repair utility (isamchk). All data saved in ISO8859_1 format. All comparisons for normal string columns are case insensitive. Full ISO8859_1 (Latin1) support. For example Scandinavian åäö is allowed in table and column names. Sorts by ISO8859_1 Latin1 (the Swedish way at the moment). It is possible to change this in the source by adding new sort order arrays.

Alias on tables and columns as in the SQL92 standard.

avg & count). INSERT,UPDATE and DELETE returns how many rows were affected. Function names do not clash with table or column names. For example ABS is a valid column name. The only restriction is that space is not allowed between a function name and the ’(’ when using functions. All MySQL commands have --help or -? for help. The server currently supports error messages to clients in many languages. See section What languages are supported by MySQL. [p 8] .

The clients uses a TCP connection or unix socket when connecting to the MySQL server. User commands as show tables, show keys from table and show columns from table What is the current MySQL version? You can always check http://www.tcx.se/ for the latest version of MySQL. How do I get MySQL? On the Internet, try using a web browser to http://www.tcx.se/ Or ftp to ftp://ftp.sunet.se/pub/unix/databases/relational/mysql/. That isSunet’s (Swedish University Network) FTP archive in Sweden. 7

Should I get MySQL in source or binary distribution? If you want to read (and/or modify) the C and C++ code that makes up MySQL you should always get a source distribution.

The code is always the ultimate manual. The source distribution also contains more tests and examples than the binary distribution. For most people who want to run MySQL on a platform that has binary releases, a binary version of MySQL is more convenient. However, TcX’s binary release is not compiled in the same way as the source release so there are some differences in where support files are located. Which operating systems does MySQL support?

We use GNU autoconf so it will be possible to port to all modern systems with working Posix threads and a C++ compiler. The client code requires C++ but not threads. We use the software ourselves primarily on Solaris (currently 2.5.1) and some on RedHat Linux 4.2 (kernel 2.0.30). A working Posix thread library is needed for the server. On Solaris 2.5 we use SUN PThreads (the native thread support in 2.4 and earlier versions are not good enough) and on Linux we use Linux Threads by Xavier Leroy @email{Xavier.Leroy@inria.fr}.

A good web page about different thread implementations is http://www.humanfactor.com/pthreads/.

The MySQL distribution includes a patched version of Provenzano’s Pthreads from MIT (see http://www.mit.edu:8001/people/proven/pthreads.html) in thedistribution. This can be used for some operating systems that does not have posix threads. We have also tried to use another user level thread package named FSU Pthreads (see http://www.informatik.hu-berlin.de/~mueller/pthreads.html). Thisimplementation is being used for the SCO port.

See the thr_lock and thr_alarm programs in the mysys directory for some tests/examples of these problems. More information can be found in the ‘PORTING’ file in the distribution. What languages are supported by MySQL. mysqld can give error messages in the following languages: Czech, Dutch, English (default), French, German, Norwegian, New Norwegian, Polish, Portuguese, Spanish and Swedish. To start mysqld with a language use the --language=lang or -L lang switch: mysqld --language swedish mysqld --language /usr/local/share/swedish The language files are located (by default) in ‘mysql_base_dir/share/LANGUAGE/’ 8

How/when will you release updates? We are going to use the following policy when updating MySQL: Each minor patch will increment the last number in the version string. When there are new features or minor incompatibilities with previous versions, the second number in the version string will be incremented. On the rare occasions when a fatal bug is found that can’t be avoided we will make new binary releases for Solaris & Linux as soon as possible. Other people may make binary releases for other systems but probably less frequently.

For other fatal bugs we will make patches available as soon as we have located and fixed the bug.

For non crucial but annoying bugs we will make patches available if they are sent to me, otherwise we will combine many of them into a bigger patch. When there are more then about 10 patches we will make a new full source release. When we have made a lot of changes we will make a new source and binary release. (About once a month?) What is UNIREG ? Unireg is our tty interface builder, but it uses a low level connection to our NISAM (with is used by MySQL) and because of this it is very quick. It has existed since 1979 (on Unix in C since ~1986). Unireg has the following components: One table viewer with updates/browsing.

Multi table viewer (with 1 scrolling region) Table creator. (With lots of column tags you can’t create with MySQL) This is WYSIWYG (for a tty). You design a screen and Unireg prompts for the column specification. Report generator A lot of utilities (Quick export/import of tables to/from text files, analysis of table contents...) Powerful multi table updates (which we use a lot) with a BASIC like language with LOTS of functions.

Dynamic languages (at present in Swedish and Finnish). If somebody wants an English version there are a few files that would have to be translate. The ability to run updates interactively or in a batch. Emacs like key definitions with keyboard macros. All this in a binary of 800k. The convform utility. Changes .frm and text files between different character sets. The pack_isam utility. Packs a NISAM table (makes it 50-80% smaller). The table can be read by MySQL like an ordinary table. Only 1 record has to be decompressed / access. Cannot handle BLOB:s or updates (yet).

We update most of our production databases with the UNIREG interface and serve web pages through MySQL (and in some extreme cases the UNIREG report generator).

Unireg takes about 3M of disk space and works on at least the following platforms: SUN OS 4.x, Solaris, Linux, HPUX, ICL Unix, DNIX, SCO and MSDOS. 9

Unireg is currently only available in Swedish and Finnish. The price tag for UNIREG is 10,000 Swedish kr (about 1500$ US), but this includes support. UNIREG is distributed as a binary. (But all the ISAM sources can be found in MySQL). Usually we compile the binary for the customer at their site. All new development is concentrated to MySQL. General SQL information and tutorials There is one SQL tutor on the net ata http://w3.one.net/~jhoffman/sqltut.htm This one has been recommended by a lot of people on the MySQL mailing list. Judith S. Bowman, Sandra L. Emerson and Marcy Darnovsky "The Practical SQL Handbook: Using Structured Query Language" Second Edition Addison Wesley ISBN 0-201-62623-3 http://www.awl.com And another book also recommended by people on the MySQL mailing list.

Understanding SQL ISBN 0-89588-644-8 Publisher Sybex 510 523 8233 Alameda CA USA What are stored procedurs and triggers and so on A stored procedure is a couple of SQL commands that can be stored and compiled in the server. After this the client doesn’t have to issue the hole query but can refer to the stored procedure. This gives some more speed because the query only have to be parsed once and there is less data that has to be sent between the server and the client. You can also raise the conceptual level by having libraies of functions in the server.

A trigger is a stored procedure that is invoked when something happens. For example one can install a stored procedure that checks every delete to a transaction table and does a automatic delete on the corresponding customer when all his transactions are deleted. Go to the first [p 5] , previous [p 5] , next [p 11] , last [p 87] section, table of contents [p 1] . 10

Go to the first [p 5] , previous [p 6] , next [p 13] , last [p 87] section, table of contents [p 1] . MySQL mailing lists and how to ask questions Subscribing to/un-subscribing from the MySQL mailing list.

Requests to be added or dropped from the MySQL list should be sent to the electronic mail address mdomo@tcx.se. Sending a one linemessage saying either subscribe mysql or un-subscribe mysql will suffice. If your reply address is not valid you may use subscribe mysql your@address.your-domain or un-subscribe mysql your@address.your-domain.

Please do not send mail about [un]subscribing to mysql@tcx.se since any mail sent to this address isautomatically forwarded to hundreds of other users. Your local site may have many subscribers to MySQL. In that case, it may have a local mailing list, so that a single message from tcx.se is sent to the site and propagated to the local list. In such cases, please contact your system administrator to be added to or dropped from the local MySQL list. Mail to mdomo is handled automatically by majordomo. Asking questions or reporting bugs.

Before you ask a question on the mailing list it is a good idea to check in the manual.

If you can’t find an answer in the manual, check with your local MySQL expert. If you do not have any luck there, read through this manual. If you still can’t find an answer to your question go ahead and send mail to mysql@tcx.se. I think I have found a bug. What information do you need to help me? If you can, please use the mysqlbug script that can be found in the scripts directory in the distribution. If that is not possible, remember to specify (if relevant) the following: 1. State which version of MySQL you are using (for example mysql-3.20.0.tgz). You can find out which version you are running by typing mysqladmin version.

2. The manufacturer and model of machine you are working on. 3. The operating system. For most operating systems you can get this from uname -a. 4. Sometimes the amount of memory (real and virtual) is also relevant. 5. If this is a bug when compiling: Include the exact error messages and also a few lines around the offending code in the file from which you got the error. 6. If this is a run time bug, please describe exactly how you got the error. If you can include a test program which shows the error you can get a more explicit answer.

If you are a support customer, please post the bug report to the specified mailing list for higher priority treatment.

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When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarise the answers and mail them to the mailing list. Guidelines for answering questions on the mailing list. Try to make your answer broad enough that people other than the original poster may benefit from it. If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. In such cases, please make sure that your answer is not a duplication of a previous answer.

Try to summarise the essential part of the question in your reply, but don’t feel obliged to quote the whole question.

Go to the first [p 5] , previous [p 6] , next [p 13] , last [p 87] section, table of contents [p 1] . 12

Go to the first [p 5] , previous [p 11] , next [p 19] , last [p 87] section, table of contents [p 1] . When do I have/want to pay for MySQL? Basic licensing issues: The easiest way to pay for MySQL is to use the license form at TcX’s secure server at @url{https://www.tcx.se/license.htmy} We hope everybody understands that you only have to pay if you are selling MySQL directly or selling a product which includes the MySQL server. You may not include MySQL in a distribution if you charge for some part of it. For internal use you do not have to pay us if you do not want to.

The client code is in the Public Domain or under the GPL (read-line).

So there should not be any problems with client code in commercial programs. We may add some additional functionality in the commercial version. The likely test candidate for this is fast compressed read only databases. The current server includes support to read such databases but not the packing tool. If we get enough revenue from support we will probably release this under the same license as the other stuff. But if you like MySQL and want to encourage further development you are welcome to purchase a license or support.

For more information see the rest of this chapter and the file ‘PUBLIC’ in the distribution. How much does MySQL cost? For normal use MySQL costs nothing. When you sell MySQL directly or as a part of another product you have to pay for it. See the file ‘PUBLIC’ in the distribution. The client access part of MySQL is in the public domain. The command line client includes parts that is under the GNU Public License (readline). These are our current license prices. All prices in US Dollars. If you pay by credit card the currency is FIM (Finish Marks) so the prices will differ slightly.

Number of licenses Price/Copy Total 1 US $200 US $200 10 pack US $150 US $1500 50 pack US $120 US $6000 For high volume (OEM) purchases the following apply: 13

licenses Price/Copy Minimum at one time Minimum Payment 100-1000 $40 100 $4000 1000-2500 $25 200 $5000 2500-5000 $20 400 $8000 The OEM prices require that you act as a middle-man for eventual problems/extension requests from users. We also require that the OEM customer has a support contract. If you have a low margin high volume product you can always talk to us about other terms. If you do, please be informative about your product, pricing, market and any other information that may be relevant. How do I get comercial support A full price license includes really basic support. This means that we are trying to answer any relevant question.

If the answer is in the documentation, we are going to direct you to the relevant documentation. If you do not have a license/support we will probably not answer at all. If you discover what we consider a real bug, we are likely to fix it in any case. But if you pay for support we will notify you about the fix status instead of just fixing it in a later release. More comprehensive support is sold separately: Types of comercial support ‘basic email support’ One year of basic email support costs $200. And includes 1. For MySQL specific questions that doesn’t belong to the mysql mailing list (@email{mysql@tcx.se}) you can contact mysql-support@tcx.se.

Remember to give your registration numberand expiration date when mailing any list to ensure a quick responce. 2. We guaranty a timely answer for your mails. We can’t garanty that we can solve any problem, but at least you will receive an answer if we can contact you by email. 3. Your suggestions for the further development of MySQL will be taken into consideration. By taking email support you have already helped the further devolpment of MySQL. If you want to have more input upgrade to extended support.

4. You are entitled to upgrade to extended email support for the difference between the different support prices. If you have extend email support you are allowed ’sligtly alter the MySQL TODO’, your email will be even more prioritized and if you have a very specific problem we can try to log in on your system and try to solve it ’in place’. ‘extented email support’ One year of extented email support costs $1000. 1. For MySQL specific questions that doesn’t belong to the mysql mailing list (@email{mysql@tcx.se}) you can contact mysql-support@tcx.se. Remember to give your registration numberand expiration date when mailing any list to ensure a quick responce.

2. We guaranty a timely answer for your mails. We can’t garanty that we can solve every problem, but at least you will receive an answer if we can contact you by email. 3. Your suggestions for the further development of MySQL will be taken into consideration. By taking extended email support you have already helped the further devolpment of MySQL.

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4. You are allowed to alter the MySQL TODO. 5. Your email will be dealt with before normal email support users and non registred users. 6. If you have a very specific problem we can try to log in on your system and try to solve it ’in place’. ‘login support’ One year of email/phone/telnet support costs $2000. In this we include support for fast compressed read only databases (no blobs yet). The current server includes support to read such databases but not the packing tool. If we get enough revenue from support we will probably release this under the same license as the server sometime in the future...

‘extented login supprt’ One year of extented email/phone/telnet support costs $5000. This of course also includes the compressed read only database support.

General terms for all types of support: How do I pay for a license? Well currently we can take SWIFT payments, cheques or credit cards. Payment should be made to: Postgirot Bank AB 105 06 STOCKHOLM, SWEDEN T.C.X DATAKONSULT AB BOX 6434 11382 STOCKHOLM SWIFT address: PGSI SESS Account number: 96 77 06 - 3 Specify: license and/or support and your name and email address. In Europe and Japan you can use EuroGiro (that should be cheaper) to the same account. If you want to pay by cheque make it payable to "Monty Program KB". And mail it to the address below.

Monty Program KB Michael Widenius Gamla Skomakarbolev.

1 E 11 00740 Helsingfors Finland If you want to pay with credit card over Internet you can use https://www.tcx.se/license.htmy Who do I contact when I want support/a license? For commercial licensing or if you have any questions about any of the information in this document, please contact: 15

Detron HB David Axmark Kungsgatan 65 B 753 21 UPPSALA SWEDEN Voice Phone +46-18-10 22 80 Fax +46-8-729 69 05 (I prefer email if possible as the fax machine happens to be in another town.) E-Mail: mysql-c@detron.se What Copyright does MySQL use? There are four different copyright’s on the MySQL distribution. 1. The MySQL specific source needed to make the mysqlclient library and programs in the ‘client’ directory is in the public domain. Each file which is in the public domain has a header which clearly states so. This is everything in ‘client’ directory and some parts of mysys, mystring and dbug libraries.

2. Some small parts of the source (GNU getopt) are covered by the "GNU LIBRARY GENERAL PUBLIC LICENSE". See the ‘mysys/COPYING.LIB’ file. 3. Some parts of the source (GNU readline) are covered by the "GNU GENERAL PUBLIC LICENSE". See the ‘readline/COPYING’ file. 4. Some parts of the source (the regexp library) are covered by a Berkeley style copyright. 5. The other source needed for the MySQL server is AGPL. See the file PUBLIC for more info. Our philosophy behind this is: The SQL client library should be totally free so it can be included in commercial products without limitations.

People who want free access to the software we have put a lot of work into can have it so long they do not try to make money directly by distributing it for profit.

People who want the right to keep their own software proprietary, but also want the value from our work, can pay for the privilege. That means that normal in house use is FREE. But if you use it for something important to you, you may want to support further development of MySQL by purchasing a support license. When may I distribute MySQL commercially without a fee This is a clarification of the information in the ‘PUBLIC’ file. MySQL may be *used* freely, including by commercial entities for evaluation or unsupported internal use. However, *distribution* for commercial purposes of MySQL, or anything containing or derived from MySQL in whole or in part, requires a written commercial license from TcX AB, the sole entity authorised by to grant such licenses.

You may not include MySQL "free" in a package containing anything for which a charge is being made except as noted below. The intent of the exception provided in the second clause is to allow commercial organisations operating an FTP server or a bulletin board to distribute MySQL freely from it, provided that: 16

1. The organisation complies with the other provisions of the FPL, which include among other things a requirement to distribute the full source code of MySQL and of any derived work, and to distribute the FPL itself along with MySQL; 2. the only charge for downloading MySQL is a charge based on the distribution service and not one based on the content of the information being retrieved (i.e., the charge would be the same for retrieving a random collection of bits of the same size); 3.

the server or BBS is accessible to the general public, i.e., the phone number or IP address is not kept secret, and anyone may obtain access to the information (possibly by paying a subscription or access fee that is not dependent on or related to purchasing anything else). If you want to distribute software in a commercial context that incorporates MySQL and you do *not* want to meet these conditions, you should contact TcX AB to find out about commercial licensing. Commercial licenses involve a payment, and include support and other benefits. These are the only ways you legally can distribute MySQL or anything containing MySQL: either by distributing MySQL under the requirements of the FPL, or by getting a commercial license from TcX AB.

I’m selling a product that can be configured to use MySQL I’m selling a product that can be configured to use MySQL although my customer is responsible for obtaining/installing MySQL (or some other supported alternative). Does one of us owe you money if my customer chooses to use MySQL?

If your product REQUIRED MySQL to work you would have to pay a license. If MySQL just added some new features it should fall inside normal use. For example is using MySQL added logging to a database instead of a text file it should not require a license. This would of course mean that the user has to fetch and install MySQL by himself. If the program is (almost) useless without MySQL you would have to get a MySQL license to sell your product. I am running a commercial web server using MySQL. Do I have to get a license for my copy? No you are not selling MySQL itself. But is this case we would like you to purchase MySQL support.

That is either your support of MySQL or our support of you (the later is more expensive since our time is limited).

Do I need a license to sell commercial perl/tcl/PHP etc applications? Is your script designed for MySQL alone? Does it require MySQL to function at all? Or is it designed for ‘a database’ and can run under MySQL, PostgreSQL, or something else? If you’ve designed it strictly around MySQL then you’ve really made a commercial product that requires the engine, so yes, I would think you have to pay. If, however, you can support any database with a base level of functionality (and you don’t rely on anything that only MySQL supports) you probably DO NOT have to pay.

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It also depends on what you’re doing for the client.

Are you tying into a database you expect to already exist by the time your software is purchased? Then you again probably don’t have to pay. Or do you plan to distribute MySQL or give them detailed instructions on installing it with your software? Then you probably do. One thing I’d like to suggest, folks. Look, development won’t last forever if nobody pays. I agree that buying a copy for every software user is prohibitive compared to other products available but would it not be courtesy for commercial developers to register their OWN copy that they develop with? Possible future changes in the licensing.

We may choose to distribute older versions of MySQL with the GPL in the future. However these versions will be identified as "GNU MySQL". Also all copyright notices in the relevant files will be changed to the GPL. Go to the first [p 5] , previous [p 11] , next [p 19] , last [p 87] section, table of contents [p 1] . 18

Go to the first [p 5] , previous [p 13] , next [p 24] , last [p 87] section, table of contents [p 1] . How standards compatible are MySQL What extension has MySQL to ANSI SQL92? The following are useful extensions in MySQL that you probably will not find in other SQL:s.

Be warned that if you use this your code will not be portable to other SQL servers. The field types MEDIUMINT, SET, EMUN???? and the different BLOB and TEXT types. The field attributes auto_increment, unsigned and zerofill. MySQL maps all tables to filenames and with MySQL one can use standard system tools to backup, rename, move, delete and copy tables. This forces MySQL to be case sensitive on table names on operating systems that have case sensitive filenames (like most Unix systems). If you have a problem remembering table names, create everything in lowercase. Use of INTO OUTFILE and STRAIGHT_JOIN in a SELECT statement.

See section SELECT syntax [p 39] .

EXPLAIN SELECT to get a description on how tables are joined. Use of key names, keys on a subpart of a field, and use of KEY or INDEX in a CREATE TABLE statement. See section CREATE TABLE syntax. [p 36] Use of DROP column or CHANGE column in a ALTER TABLE statement. See section ALTER TABLE syntax [p 37] . Use of LOAD DATA INFILE. This syntax is in many cases compatible with Oracles LOAD DATA INFILE. See section LOAD DATA INFILE syntax [p 45] . Using " instead of ’ to enclose strings. Using the escape \ character.

The SET OPTION statement. See section SET OPTION syntax. [p 48] Using, in the SELECT part of a GROUP BY statement, fields or functions that do not appear in the GROUP BY list.

In MySQL this means ’any matching value’. By using this one can get a much higher performance by avoiding sorting and grouping unnecessary items. This is often used in this context: SELECT order.customerid,customer.name,max(payments) from order,customer WHERE order.customerid = customer.customerid GROUP BY order.customerid; In ANSI SQL you would have to add the customer.name in the GROUP BY clause which is redundant in MySQL.

To make it easier for user that comes from different SQL environments mysql supports a lot of aliases for many functions. For example all string functions support both the ANSI SQL and the ODBC syntax. The || and && operators is in MySQL synonyms for OR and AND, like in the C programming language. Likewise | and & stands for bitwise OR and AND. Because if this nice syntax, MySQL doesn’t support the ANSI SQL operator || for string concatenation, but one have to use CONCAT() instead. As CONCAT() takes any number of arguments it’s easy to convert use of the || operatior to MySQL.

Use of any of the following functions: , AND, OR, or LIKE in a column statement LAST_INSERT_ID.

See section How can I get the unique ID for the last row? [p 83] 19

REGEXP or NOT REGEXP. CONCAT() or CHAR() with 1 or more than 2 arguments. In MySQL the above functions can take any number of arguments. BIT_COUNT(), ELT(), FROM_DAYS(), FORMAT(), IF(), PASSWORD(), ENCRYPT(), PERIOD_ADD(), PERIOD_DIFF(), TO_DAYS(), or WEEKDAY(). Use of TRIM to trim substrings. ANSI SQL only supports removal of single characters. The STD(), BIT_OR and BIT_AND group functions. Use of MIN() or MAX() as functions, not group functions. What functionality is missing in MySQL. The following functionality is missing in the current version of MySQL. For the priority of new extensions you should consult: http://www.tcx.se/TODO Sub-SELECT.

The following will not work in MySQL: SELECT * from table WHERE id IN (SELECT id from table2) MySQL only supports INSERT ... SELECT.... Independent sub-SELECTs will be availably in 3.22.0. One can use the function IN() in other context thought. MySQL doesn’t yet support sqlSELECT ... INTO TABLE . Currentlyl MySQL only supports SELECT ... INTO OUTFILE....

Outer joins. LEFT OUTER JOIN will be availabe in 3.22.0. Transactions is not supported. MySQL will shortly support atomic operations which is like transactions without rollback. With atomic operations you can make a bunch of insert/select/whatever commands and be guaranteed that no other thread will interfere. In this context you won’t usually need rollback. Currently you can do this with the help of the LOCK TABLES/UNLOCK TABLES command. See section Lock tables syntax [p 48] Triggers is not supported. The planed update language will be able to handle stored procedures, but without triggers.

Triggers usually slow down everything, even for queries when they aren’t needed.

The FOREIGN KEY syntax in MySQL exists only for compatibility with other SQL vendors CREATE TABLE commands: It doesn’t do anything. The FOREIGN KEY syntax without ON DELETE .. is mostly used for documentation purposes. Some ODBC applications may uses this to produce automatic WHERE clauses thought, but this is usually easy to override. FOREIGN KEY is sometimes used as a constraint check, but this check is in practice unnecessary if one insert rows in the tables in the right order. In MySQL one can go around the problem that ON DELETE ... isn’t implement by adding the approative DELETE statement to the application when one deletes record from a table that has FOREIGN KEY.

In practice this is as quick (in some case quicker) and much more portable than using FOREING KEY Foreign keys is something that makes life very complicated, because the foreign key definition must be stored in some database and then the hole ’nice approach’ by using only files that can be moved, copied and removed will be destroyed. In the near future we will extend FOREIGN KEYS so that the at least the information will be saved and may be retrieved by mysqldump and ODBC. MySQL doesn’t support views, but this is on the TODO. Some other SQL has -- as start comment. MySQL has # as the start comment character, even if the MySQL command line tool removes all lines that starts with --.

MySQL will not support this degenerated comment style because we have had many problems with automatic generated SQL queries that has used something like the following code: 20

UPDATE table_name SET credit=credit-!payment! Where instead of !payment! we automaticly insert the value of the payment. What do you think will happen when ’payment’ is negative ? Because 1--1 is legal in SQL, we think is terrible that ’--’ means start comment. If you have a sql program in a textfile that contains -- comments you should use replace < text-file-with-funny-comments.sql | mysql database. instead of the normal mysql database < text-file-with-funny-comments.sql You can also change the -- to # comments in the command file with: replace - text-file-with-funny-comments.sql and change them back with: replace - text-file-with-funny-comments.sql What standards does MySQL follow? Entry level SQL92.

ODBC level 0-2. What functions exist only for compatibility? GRANT. See section GRANT syntax. (Compatibility function). [p 49] This always succeeds. You should use the MySQL privilege tables. See section How does the privilege system work? [p 26] CREATE INDEX. See section CREATE INDEX syntax (Compatibility function). [p 49] This always succeeds. You should create your index with CREATE TABLE. See section CREATE TABLE syntax. [p 36] You can also use ALTER TABLE. See section ALTER TABLE syntax [p 37] .

DROP INDEX. See section DROP INDEX syntax (Compatibility function). [p 49] This always succeeds. You can use ALTER TABLE to drop indexes. See section ALTER TABLE syntax [p 37] . Limitations of BLOB and TEXT types If you want to GROUP BY or a ORDER BY on a BLOB or TEXT field, you must make the field into a fixed length object. The standard way to do this is with the SUBSTRING functions. If you don’t do this only the first max_sort_length (default=1024) will considered when sorting. SELECT comment from table order by substring(comment,20); How to go cope without COMMIT-ROLLBACK MySQL doesn’t support COMMIT-ROLLBACK.

The problem with COMMIT-ROLLBACK is that for it to handle this efficiently it would require a completely different table layout than MySQL uses today. MySQL would also need extra threads that does automatic cleanups on the tables and the disk usage space needed would be much higher. This would make MySQL about 2-4 times slower than it is today. One of the reasons that MySQL is so much faster than almost all other SQL databases 21

(typical times are at least 2-3 times faster) is the lack of COMMIT-ROLLBACK. For the moment, we are much more for implementing the SQL server language (stored procedures). With this you very seldom really need COMMIT-ROLLBACK besides being able to do many more things without losing any speed. Loops that need transactions can normally be coded with the help of LOCK TABLES and one doesn’t need cursors when one can update records on the fly. We have transactions and cursors on the TODO but not quite prioritised. If it is implemented it will be as a option to CREATE TABLE. That means that COMMIT-ROLLBACK will only work on those tables and only those tables will be slower.

We at TcX have a greater need for a real fast database than a 100% general database. Whenever we find a way to implement these without any speed loss we will probably do it, but for the moment there is many more important things to do. Check the TODO for how we prioritise things at the moment. Customers with extended mail support can alter this slightly, so things may be reprioritised. The current problem is actually ROLLBACK. Without ROLLBACK you can do anything with LOCK TABLES. To support ROLLBACK MySQL would had to be changed to store all old records that was updated and revert everything back to the starting point if ROLLBACK was issued.

For simple cases this isn’t that hard to do (the current isamlog could be used for this), but if one wants to have ROLLBACK with ALTER/DROP/CREATE TABLE it would make everything much harder to implement.

To avoid using ROLLBACK one can do: LOCK TABLES ... - Test conditions. - Update if everything is ok. UNLOCK TABLES. This is usually much faster, but not always. The only thing this doesn’t handle if someone does a kill on the process... One can also use functions to update things in one operation. By doing all updates relatively and/or only update those fields that actually have changed one can get a very efficient application. For example, when we are doing updates on some customer information, we only update the customer data that has changed and only test that not any of the changed data, or data that depends on the changed data, has changed in the original row.

The test for change is down with the WHERE clause in the UPDATE statement. If the record wasn’t updated we give the client a message: "Some of the data you have changed has been changed by another user", and then we show the old row versus the new row in a window. The user can then decide which version of the customer record he should use. This gives us something like ’column locking’ but actually even better, because we only update some of the columns with relative information. This means that a typical update statement looks something like: 22

UPDATE tablename SET pay_back=pay_back+’relative change’ UPDATE customer set customer_date=’current_date’, address=’new address’, phone=’new phone’, money_he_ows_us=money_he_ows+’new_money’ where customer_id=id and address=’old address’ and phone=’old phone’; As you can see, this is very efficient and even if another client has changed the ’money_he_ows_us’ or ’pay_back’ amount this will still work.

In many cases, users have wanted ROLLBACK and/or LOCK TABLES to manage unique identifiers for some tables. This can be handled much more efficiently by using an AUTO_INCREMENT column and the MySQL API function mysql_insert_id.

See section How can I get the unique ID for the last row? [p 83] At TcX we have never had any need for row level locking as we have always been able to code around it. I know some cases that really need row locking, but they are very few. If you want to have row level locking you can do something like: UPDATE table_name SET row_flag=1 WHERE id=ID ; MySQL returns affected rows = 1 if the row was found and row_flag wasn’t 1 in the original document. On the TODO there is GET_LOCK and RELEASE_LOCK for those that want to implement application level locking.

Go to the first [p 5] , previous [p 13] , next [p 24] , last [p 87] section, table of contents [p 1] . 23

Go to the first [p 5] , previous [p 19] , next [p 26] , last [p 87] section, table of contents [p 1] . Compiling and installing MySQL Compiling MySQL See the file ‘INSTALL-SOURCE’ in the MySQL distribution. Problems starting MySQL Check the log file to see if mysqld started up correctly. cd tail .log To verify that MySQL is working run the following tests: > cd /usr/local/bin > ./mysqlshow - + | Databases | - + | mysql | - + > ./mysqlshow mysql Database: mysql - + | Tables | - + | db | | host | | user | - + > ./mysql -e "select host,db,user from db" mysql - + | host | db | user | - + | test | | | test | - + There is also a benchmark suite so you can compare how MySQL perform on different platforms.

In the near future this will also be used to comapre MySQL to other SQL databases. > cd bench > run-auto-increment-test You can also run the tests in the test subdirectory. To run ‘auto_increment.tst’: ./mysql -vf test < ./tests/auto_increment.tst 24

Expected results are shown in the file ‘./tests/auto_increment.res’. Automatic start/stop of MySQL To start or stop MySQL use the following commands: scripts/mysql.server stop scripts/mysql.server start You might want to add these start and stop commands in the appropriate places in your /etc/rc* files when you start using MySQL for production applications. How to debug MySQL If you are porting MySQL to an new system you should first try to get mysys/thr_lock and mysys/thr_alarm to work. They shouldn’t core dump and not print any error (they also print a lot of other information). Also see the file ‘PORTING’ in the distribution.

By starting bin/safe_mysqld with --log you will get a log in install-directory/var/’hostname’.log (the top level database directory). This log will contain all successful connections and all commands issued to the MySQL server. If you have compiled MySQL with --with-debug=yes you can can also get a very informative log with: libexec/mysqld --debug which makes a large log in /tmp/mysql.trace. The default debug option is d:i:t:o,/tmp/mysql.trace.

You can get a smaller log with: libexec/mysqld --debug=d,info,query,general:o,/tmp/mysql.trace or an even smaller (on stdout): libexec/mysqld --debug=d,general,query You can get more information about the debug switches by examining the file dbug/dbug.c. If you have a problem with mysqld that it crashes and you want this quickly solved, you should include a trace file with your mail if possible. Trace files can be posted directly to @email{mysql-support@tcx.se} to avoid long messages to the standard mail list. If the trace file is big you should use ftp and send it to ftp://www.tcx.se/pub/mysql/secret/ together with a mysqldump of any tables that you think can help to solve the problem.

The context of the above directory is hidden for outside users so no one except the TCX staff can look at what you send into it. Go to the first [p 5] , previous [p 19] , next [p 26] , last [p 87] section, table of contents [p 1] . 25

Go to the first [p 5] , previous [p 24] , next [p 30] , last [p 87] section, table of contents [p 1] . How does MySQL privileges work MySQL has a advanded but non standard security/privileges system. How does the privilege system work? The MySQL privilege system makes sure that each user may do exactly the things that they are supposed to be allowed to do. The system decides to grant different privileges depending on which user connects from which host to which database. The decision is based on the contents of the three tables in the MySQL database: user, host and db.

The grant tables privileges on rows are select, insert, update and delete.

The table and database privileges are create and drop. Create and drop are for both tables and databases. Since a user with a drop grant can delete any table, this is the same thing as a drop grant for the database. Other privileges give the right to use files (for LOAD DATA INFILE and SELECT INTO OUTFILE) and to use the administrative commands shutdown, reload, refresh and process, to get the current process list. The privilege tables are read into mysqld with mysqladmin reload. If the privilege tables are empty or non-existent or if the server is started with --skip-grant-tables, full access is granted to everyone.

You can always test your privileges with the script mysqlaccess, which Yves Carlier has provided for the MySQL distribution. See section Why do I get ’Access denied’? [p 78] The host and db fields may contain a SQL regexp with chars % and _. Leaving any of these fields empty is equivalent to setting it to ’%’. A host may be localhost, a hostname, an IP number or an SQL expression. An empty host in the db table means any host in the host table. An empty host in the host or user table means any host that can create a TCP connection to your server.

A db is the name of a database or an SQL regexp.

An empty user field means any username will do. An empty password means that the entry will only be used if no password is supplied. The privileges from the user table are OR’ed to the db table. This means that a superuser only needs to be in the user table with all privilege-flags set to Y. Everything granted in the user table is valid for every database that cannot be found in the db table. For this reason, it might be wise to grant users (apart from superusers) privileges on a per-database basis only.

The host table is mainly there to maintain a list of "secure" servers. At TcX host contains a list of all machines on the local network. These are granted all privileges. 26

The connecting user’s privileges are calculated by the following algorithm: 1. First sort all three tables by host by putting hosts without wildcards first, followed by hosts with wildcards and entries with host . Within each host, di.e. very much like GROUP BY Host, sort by user using the same rules. Finally, in the db table, sort by db using the same rules. In the steps below, we will look through the sorted tables and always use the first match found.

2. Get the privileges for the connecting user from the db table using the first match found. Call this set of privileges P.

3. If host " for the entry found in the db table, AND P with the privileges for the host in the host table, i.e. remove all privileges that are not "Y" in both. (If host "", P is not affected. In suchcases, host must have matched the connecting host’s name at least partially. Therefor it can be assumed that the privileges found in this row match the connecting host’s profile.) 4. OR (add) P with the privileges for the user from the user table, i.e. add all privileges that are "Y" in user.

The connecting user gets the set of privileges P. Let’s show an example of the sorting and matching! Suppose that the user table contains this: + - | Host | User .

. + - | root . . | jeffrey . . | localhost | root . . | localhost . . + - Then the search order will be: localhost/root localhost/any any/jeffrey any/root So jeffrey attempting to connect on localhost will be matched by the localhost/any line, not by the any/jeffrey line. The first match found is used! So if you have access problems, print out the user table, sort it by hand, and see where the match is being made.

Here follows an example to add a user ’custom’ that can connect from hosts ’localhost’, ’server.domain’ and ’whitehouse.gov’. He wants to have password ’stupid’. The database ’bankacount’ he only want to use from ’localhost’ and the ’customer’ database he wants to be able to reach from all three hosts. shell> mysql mysql. mysql> insert into users (host,user,password) values(’localhost’,’custom’,password(’stupid’)); mysql> insert into users (host,user,password) values(’server.domain’,’custom’,password(’stupid’)); mysql> insert into users (host,user,password) values(’whitehouse.gov’,’custom’,password(’stupid’)); 27

mysql> insert into db (host,db,user,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) values (’localhost’,’bankacount’,’custom’,’Y’,’Y’,’Y’,’Y’,’Y’,’Y’); mysql> insert into db (host,db,user,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) values , ’ customers’,’custom’,’Y’,’Y’,’Y’,’Y’,’Y’,’Y’); You can of course also use xmysqladmin, mysql_webadmin, mysqladmin and even xmysql to insert/change and update values in the privilege tables. You can find these utilities in the Contrib directory.

Adding new user privileges to MySQL To add privileges to the MySQL database: This assumes the current user has insert privileges for the mysql db table and reload privileges.

The server (mysqld) has to be running. If it is not, start it with safe_mysqld --log &. > mysql mysql insert into user values , ’ monty’,password(’something’),’Y’,’Y’,’Y’,’Y’,’Y’,’Y’,’Y’,’Y’,’Y’,’Y’) ; insert into user (host,user,password) values(’localhost’,’dummy ; insert into user values , ’ admin’,",’N’,’N’,’N’,’N’,’N’,’N’,’Y’,’N’,’Y’,’Y’) ; quit > mysqladmin reload This makes three new users: Monty Full superuser, but must use password when using MySQL. admin Doesn’t need a password but is only allowed to use mysqladmin reload, mysqladmin refresh and mysqladmin processlist. May be granted individual database privileges through table db.

dummy Must be granted individual database privileges through table db. Default privileges. The default privileges (set in ‘scripts/mysql_install_db’) is that root can do anything. Any user can do anything with any database whose name is ’test’ or starts with ’test_’. A normal user can’t use mysqladmin shutdown or mysqladmin processlist. See the script (‘scripts/mysql_install_db’) for an example on how to add other users. The privilege tables are read into mysqld with ’mysqladmin reload’. If the privilege tables are empty (or non-existent) full access are granted to everyone.

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A example of permission setup.

A common mistake is to try something like: INSERT INTO user VALUES , ’ jeffrey’,’bLa81m0’,’Y’,’Y’,’Y’,’N’,’N’,’N’,’N’,’N’, ’N’,’N’); Then (of course) a mysqladmin reload to make the authentication change take effect, then trying to connect to the server: $ ./mysql -h sqlserver -u jeffrey -p bLa81m0 test Access denied Try this instead: INSERT INTO user VALUES , ’ jeffrey’,password(’bLa81m0’),’Y’,’Y’,’Y’,’N’,’N’,’N’,’N’,’N’,’N’,’N’); And like before mysqladmin reload to make the authentication change take effect.

Now things should work. Go to the first [p 5] , previous [p 24] , next [p 30] , last [p 87] section, table of contents [p 1] . 29

Go to the first [p 5] , previous [p 26] , next [p 52] , last [p 87] section, table of contents [p 1] . MySQL language reference Literals. How do you write strings and numbers? STRINGS A string may have ’ or " around it. \ is a escape character. The following escape characters are recognised: \0 A ascii 0 character. \n A newline character. \t A tab character. \r A return character. \b A backspace character. \’ A ’ character.

\" A " character. \\ A \ character. \% A % character. This is used in wild-card strings to search after %. \_ A _ character. This is used in wild-card strings to search after _. A ’ inside a string started with ’ may be written as ". A " inside a string started with " may be written as "". MySQL> select ’hello’, "’hello " " hello " ’ h"e"l"l"o"’, "hel""lo"; 1 rows in set (0.00 sec) - + | hello | ’hello " " hello ’ h’e’l’l’o’ | hel"lo | - + | hello | ’hello " " hello ’ h’e’l’l’o’ | hel"lo | - + mysql> select ’hello’, "hello " " hello " ’ ello", ’e"l"lo \ ’ hello’; 1 rows in set (0.00 sec) - + | hello | hello | ""hello ’ ello | e’l’lo | ’hello | - + | hello | hello | ""hello ’ ello | e’l’lo | ’hello | - + mysql> select "This\nIs\nFour\nlines"; 1 rows in set (0.00 sec) - + | This Is Four lines | - + | This 30

Is Four lines | - + If you want to insert binary data into a blob the following characters must be represented by escape sequences: \0 Ascii 0. Should be replaced with "\0" (A backslash and a 0 digit). \ Ascii 92, backslash ’ Ascii 39, Single quote " Ascii 33, Double quote NUMBERS Integers are just a sequence of digits. Floats use . as a decimal separator. Examples of valid numbers are: 1221, 294.42, -32032.6809e+10. NULL When using the text file export formats, NULL may be represented by \N. See section LOAD DATA INFILE syntax [p 45] Column types.

The following column types are supported: Name Description Size TINYINT [(max display size)] [UNSIGNED] [ZEROFILL] A very small integer.

Signed range -128 - 127. Unsigned range 0 - 255. 1 SMALLINT [(max display size)]. [UNSIGNED] [ZEROFILL] A small integer. Signed range -32768 - 32767. Unsigned range 0 - 65535. 2 MEDIUMINT [(max display size)] [UNSIGNED] [ZEROFILL] A medium integer. Signed range -8388608-8388607. Unsigned range 0 - 16777215. 3 INT [(max display size)] [UNSIGNED] [ZEROFILL] A normal integer. xSigned range -2147483648 - 2147483647. Unsigned range 0 - 4294967295. 4 BIGINT [(max display size)] [UNSIGNED] [ZEROFILL] A large integer. Signed range -9223372036854775808 - 9223372036854775807. Unsigned Range 0 - 18446744073709551615.

8 31

FLOAT(Precision) A small floating point number. Precision can be 4 or 8. FLOAT(4) is a single precision number and FLOAT(8) is a double precision number (se the DOUBLE entry). This syntax is for ODBC compatibility. Range -3.402823466E+38F - -1.175494351E-38, 0, -1.175494351E-38 - 3.402823466E+38F. 4 FLOAT [(max display size,number of decimals)] A small floating point number. Cannot be unsigned. Range -3.402823466E+38F - -1.175494351E-38, 0, -1.175494351E-38 - 3.402823466E+38F. 4 DOUBLE PRECISION [(max display size,number of decimals)] A normal floating point number.

Cannot be unsigned. Range -1.7976931348623157E+308 - -2.2250738585072014E-308, 0, 2.2250738585072014E-308 - 1.7976931348623157E+308. 8 REAL [(length,decimals)] Same as DOUBLE 8 DECIMAL [(max display size,number of decimals)] An unpacked floating point number. Cannot be unsigned. Currently the same range maximum range as a double. Behaves as a CHAR column M+D NUMERIC [(length,decimals)] Same as DECIMAL M+D TIMESTAMP [(display size)] An automatic timestamp. 4 DATE A type to store date information. Uses the "YYYY-MM-DD" syntax, but may be updated with a number or a string. Understands at least the following syntaxes: ’YY-MM-DD’, ’YYYY-MM-DD’, ’YYMMDD’, ’YYMM’, ’YY’.

Range 0000-00-00 to 9999-12-31. 4 TIME A type to store time information. Uses the "HH:MM:SS" syntax, but may be updated with a number or a string. Understands at least the following syntaxes: ’HH:MM:DD, ’HHMMDD’, ’HHMM’, ’HH’. 3 DATETIME A type to store date and time information. Format "YYYY-MM-DD HH:MM:SS". Takes 8 bytes. Range ’0000-01-01 00:00:00’ - ’9999-12-31 23:59:59’. 8 CHAR(max_length) [binary] A fixed length string that is always filled up with spaces to the specified length. Range 1 - 255 characters. All end space are removed when retrieved. Is sorted and compared case insensitively unless the binary keyword is given.

M VARCHAR(max_length) [binary] A variable length string that is stored with its length. Maximum range 1 - 255 characters. Is sorted and compared case insensitively unless the binary keyword is given. L + 1 TINYTEXT and TINYBLOB A TEXT/BLOB with max length of 255 characters. L + 1 TEXT and BLOB A TEXT/BLOB with max length of 65535 characters. L + 2 32

MEDIUMTEXT and MEDIUMBLOB A TEXT/BLOB with max length of 1677216 characters. L + 3 LONGTEXT and LONGBLOB A TEXT/BLOB with max length of 4294967295 characters. L + 4 ENUM(’value’,’value2 . ) A string object that can have only one set of allowed values. See section More about data types [p 33] . 1 or 2 SET(’value’,’value2 . ) A string object that can have one or many values of a set of allowed values. See section More about data types [p 33] . 1-8 More about data types Database size info. In the above table L means the actual length of a instance and M the maximum length. So L+1 for "abcd" means 5 bytes in the database.

If you use any data type with a L in the length field you will get a variable length record format. The numeric types All integer types can have a optional argument unsigned. This can be used when you only want to allow positive numbers in the column or you need a little bigger numerical range for the column. Also for all integer columns the optional argument ZEROFILL means that the column will be padded with zeroes upto the maximum length. Max display size and decimals are for formating and calculation of max column width. TIMESTAMP type Has a range of 1 Dec 1970 time 0.00 to sometime in the year 2106 and a resolution of one second.

Will be automatically updated if not used in a statement that updates a row or if set to NULL. Can be a (part of) a key. Note that if you have many timestamp fields in a row, then only the first timestamp field will be automatically updated. Any timestamp field will be set to the current time if set to NULL. Depending on the display size one gets one of the following formats: "YYYY-MM-DD HH:MM:SS", "YY-MM-DD HH:MM:SS", "YYYY-MM-DD" or "YY-MM-DD". TEXT and BLOB types These are objects that can have a variable length without upper limit. All TEXT and BLOB objects are stored with is length (saved in 1 to 4 bytes depending on the type of object).

The maximum TEXT and BLOB length you can use is dependent on available memory and client buffers. The only differences between TEXT and BLOB is that TEXT is sorted and compared case insensitively while BLOB is compared case insensitive (by character values). TEXT and BLOB objects CANNOT be keys. A BLOB is a binary large object which can hold any amount of data :) There are 4 kinds of blobs See section Column types. [p 31] . Normally one can regard a BLOB as a VARCHAR without a specified limit.

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TEXT is a BLOB that is sorted and compared case insensitively. There are some constraints because of the message buffer used. The default size of the buffer is 64K for the server and 512K for the clients. To change the buffer length for the server, use mysqld -O max_allowed_packet=max_blob_length. This allows the message buffer to grow up to this limit when needed. MyODBC defines BLOB:s as LONGVARBINARY and TEXT:s as LONGVARCHAR. Restrictions for BLOB and TEXT columns: 1. A BLOB or TEXT cannot be a key or a part of a key 2. When one sorts or groups a BLOB or TEXT only the first max_sort_length (default 1024) of the blob is used.

This value can be changed by the -O option when starting the mysqld demon. One can group on an expression involving a BLOB/TEXT: SELECT id,SUBSTR(blob,1,100) GROUP BY 2 3. There is no end space truncation for BLOB and TEXT as there is for CHAR and VARCHAR. ENUM type A string object that can have only one set of allowed values. The value to be stored may be given case independently. If one tries to store a non existing value, "" is stored. If used in a number context this object returns/stores the value index. If there is less than 255 possible values this object occupies 1 byte, else two bytes (with a maximum of 65535 different values).

Note that if a integer is put in the ENUM you get the corresponding string with the first counting as number zero. Sorting on ENUM types are done after the order of the strings in the enum.

For example the column test ENUM("one","two", "three") can have any off these values: "one" "two" "three" SET type A string object that can have one or many values of a set of allowed values. Each value is separated by a . If used in a number context this object returns/stores the bit positions of the used values. This object occupies (number_of_different_values-1)/8+1 bytes, rounded up to 1,2,3,4 or 8. One can’t have more than 64 different values. Note that if a integer is put in the SET you get the corresponding string with the first bit corresponding to the first string.Sorting on SET types are done numericaly.

For example the column test SET("one","two") can have any off these values: "" "one" "two" "one,two" 34

Column indexes You can have indexes on all MysQL column types except BLOB and TEXT. Using indexes on the relevant columns is the most important thing is getting you selects to run fast. For CHAR and VARCHAR columns you can have a index on a prefix. The example below show how to create a index for the first 10 characters of a column. This is much faster and requires less disk space than having a index on the whole field. CREATE TABLE test ( name CHAR(200), KEY name (last_name(10)); Multiple field indexes MySQL can have one index on parts of different columns. A multiple column key can be considered as a sorted array where the columns are concatenated.

Suppose that you have a table: CREATE TABLE test ( id INT, last_name CHAR(30), first_name CHAR(30), PRIMARY KEY (id), KEY name (last_name,first_name)); Then the key ’name’ is a key over last_name and first_name. The ’name’ key will be used in the following queries: SELECT * FROM test WHERE last_name="Widenius"; SELECT * FROM test WHERE last_name="Widenius" AND first_name="Michael"; SELECT * FROM test WHERE last_name="Widenius" AND (first_name="Michael" OR first_name="Monty"); SELECT * FROM test WHERE last_name="Widenius" and first_name >="M" and first_name < "N"; The ’name’ key will NOT be used in the following queries: SELECT * FROM test WHERE first_name="Michael"; SELECT * FROM test WHERE last_name="Widenius" or first_name="Michael"; Type mapping (to ease moving tabel definitions between different databases engines) To support easier use of code from different SQL vendors, MySQL does supports the following mappings: 35

binary(num) char(num) binary char varying varchar float4 float float8 double int1 tinyint int2 smallint int3 mediumint int4 int int8 bigint long varbinary blob long varchar text middleint mediumint varbinary(num) varchar(num) binary CREATE TABLE syntax. CREATE TABLE table_name ( create_definition ) create_definition: column_name type [DEFAULT default_value] [NOT NULL | NULL] [ PRIMARY KEY ] [reference_definition] or PRIMARY KEY ( key_column_name ) or KEY [key_name] KEY( key_column_name,...) or INDEX [key_name] ( key_column_name,...) or UNIQUE [key_name] ( key_column_name,...) or FOREIGN KEY key_name ( key_column_name [ reference_definition] or CHECK (expr) key_column_name: column_name [ (length) ] reference_definition: REFERENCES table_name [( key_coulmn_name ) ] [ MATCH FULL | MATCH PARTIAL] [ ON DELETE reference_option] [ ON UPDATE reference_option] reference_option: RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT The FOREIGN KEY, CHECK and REFERENCE syntax are only for compatibility.

They don’t actually do anything.

If a column doesn’t have a DEFAULT value and is not declared as NOT NULL, the default value is NULL. 36

ZEROFILL means that number is pre-zeroed to maximal length. With INT(5) ZEROFILL a value of 5 is retrieved as 00005. BINARY means that the column will be compared case sensitive. The default is that all strings are compared case insensitive. BINARY is ’sticky’ which means that if a column marked ’binary’ is used in a expression, the whole expression is compared ’binary’. INDEX is only a synonym for KEY. If one doesn’t assign a name to a key, the key will get the same name as the first key_column with an optional _# to make it unique.

Key columns and timestamp columns can’t be NULL. For these columns the NULL attribute is silently removed. With column_name(length) syntax one can specify a key which is only a part of a string column. This can make the index file much smaller. A number column may have the additional attribute AUTO_INCREMENT to automatically get the largest value+1 for each insert where column value is NULL or 0. See section How can I get the unique ID for the last row? [p 83] One can insert NULL for timestamp and auto_increment columns. This results in the current time / the next number.

Blob columns can’t be keys.

When one groups on a blob only the first ’max_sort_length’ bytes are used See section Limitations of BLOB and TEXT types [p 21] . Deleted records are in a linked list and subsequent inserts will reuse old positions. To get smaller files one can use the isamchk utility to reorganise tables. Each null column takes 1 bit extra, rounded up to the nearest byte. The maximum record length can be calculated as follows: 1+ sum_of_column_lengths + null_columns/8 + number of variable length columns.

In some cases an attribute may silently change after creation: VARCHAR columns with a length of 1 or 2 are changed to CHAR. When using one VARCHAR column all CHAR columns longer than 2 are changed to VARCHAR’s. On INSERT/UPDATE all strings (CHAR and VARCHAR) are silently chopped/padded to the maximal length given by CREATE. All end spaces are also automatically removed. For example VARCHAR(10) means that the column can contain strings with a length up to 10 characters. Something/0 gives a NULL value.

The regular expression function (REGEXP and RLIKE) uses ISO8859-1 (Latin1) when deciding the type of a character.

ALTER TABLE syntax ALTER [IGNORE] TABLE table_name alter_specification [, alter_specification ...] alter_specification: ADD [COLUMN] create_definition or CHANGE [COLUMN] old_column_name create_definition or ALTER [COLUMN] column_name { SET DEFAULT literal | DROP DEFAULT } or DROP [COLUMN] column_name or DROP PRIMARY KEY DROP INDEX key_name ALTER TABLE works by creating a temporary table and copying all information to it and then the old table is deleted and the new one is renamed. This is done in such a way that all updates are automatically redirect to the new table without any failed updates.

While the ALTER TABLE is working, the old table is readable for other clients. Table updates/writes to the table are stalled 37

and only executed after the new table is ready. If IGNORE isn’t specified then the copy will be aborted and rolled back if there exists any duplicated unique keys in the new table. This is a MySQL extension. The CHANGE column_name, DROP column_name and DROP INDEX are MySQL extensions to ANSI SQL92. The optional word COLUMN is a pure noise word and can be omitted. The ADD and CHANGE takes the same create_definition as CREATE TABLE. See section CREATE TABLE syntax. [p 36] . ALTER COLUMN sets a new default value or removes the old default value for a column. DROP INDEX removes an index. This is an MySQL extension.

The FOREIGN KEY syntax in MySQL exists only for compatibility with other SQL vendors CREATE TABLE commands: It doesn’t do anything. See section How standards compatible are MySQL [p 19] If one drops a column_name which is part of some key, this key part is removed. If all key parts are removed then the key is removed. DROP PRIMARY KEY drops the first UNIQUE key in the table. CHANGE tries to convert data to the new format as good as possible. With mysql_info(MYSQL*) one can retrieve how many records were copied and how many records were deleted because of multiple keys.

To use ALTER TABLE one has to have select, insert, delete, update, create and drop privileges on the table.

DROP TABLE syntax. DROP TABLE table_name [, table_name....] Removes one or more tables. All the data and the definition is removed so take it easy with this command! DELETE syntax. DELETE FROM table_name WHERE where_definition Returns records affected. If one does a delete without a where clause then the table is recreated which is much faster than doing a delete for each row. In these cases, the SQL command returns zero as affected records. Using DELETE FROM table_name will work even if the data files do not exist as only information from the table definition file, table_name.frm, is used.

All string comparisons are case independent with case according to ISO-8859-1 Latin1. LIKE is allowed on numerical columns.

Compare with explicit NULL (column == NULL) is the same as if IS NULL was used (column IS NULL). This is is done to be consistent with mSQL. 38

SELECT syntax SELECT [STRAIGHT_JOIN] [DISTINCT | ALL] select_expression [ INTO OUTFILE ’file_name [ FROM tables... [WHERE where_definition ] [GROUP BY column [ ORDER BY column [ASC | DESC ] HAVING where_definition [LIMIT [offset,] rows] [PROCEDURE procedure_name]] Strings are automatically converted to numbers and numbers to strings when needed (ala perl). If in a compare operation ) either if the arguments are numerical the arguments are compared as numbers, else the arguments are compared as strings.

All string comparisons are by default done case-independent by ISO8859-1 (The Scandinavian letter set which also works excellent with English).

select 1 > "6x > 0 select 7 > "6x > 1 select 0 > "x6 > 0 select 0 = "x6 > 1 A column name does not have to have a table prefix if the given column name is unique. A select expression may be given an alias which will be column name and can be used when sorting and grouping or in the HAVING clause. select concat(last_name,’ ’,first_name) as name from table order by name In LIKE expressions % and _ may be preceded with ’\’ to skip the wild-card meaning. A DATE is a string with one of the following syntaxes: YYMMDD (Year is assumed to be 2000 if YY < 70.) YYYYMMDD YY.MM.DD Where ’.’ may be any non numerical separator.

YYYY.MM.DD Where ’.’ may be any non numerical separator. IFNULL() and IF() returns number or string value according to use. ORDER and GROUP columns may be given as column names, column alias or column numbers in SELECT clauses.

The HAVING clause can take any columns or alias in the select_expressions. It is applied last, just before items are sent to the client, without any optimisation. Don’t use it for items that should be in the WHERE clause. You can’t write (yet): SELECT user,MAX(salary) FROM users GROUP BY users HAVING max(salary)>10 Change it to: SELECT user,MAX(salary) AS sum FROM users GROUP BY users HAVING sum > 10 STRAIGHT_JOIN forces the optimiser to join the tables in the same order that the tables are given in the FROM clause. One can use this to get a query to be done more quickly if the optimiser joins the tables in not optimal order.

See section EXPLAIN syntax. Get information about a SELECT. [p 47] LIMIT takes one or two numerical arguments. If one argument, the argument indicates the maximum number of rows in a result. If two arguments, the first argument says the offset to the first row to return, the second is 39

the maximum number of rows. INTO OUTFILE ’filename’ writes the given set to a file. The file can not exist from before. See section LOAD DATA INFILE syntax [p 45] . Functions A select_expression or where_definition can consist of any expression using the following functions: Group functions. ( ) Parenthesis Normal mathematical operations. + - * / A division by zero results in a NULL. Bit functions. These have a range of maximum 64 bits because MySQL uses longlong arithmetic. | & BIT_COUNT() Number of set bits in an argument. Normal logical. Returns TRUE (1) or FALSE (0). NOT !

OR AND Comparison operators.

Returns TRUE (1) or FALSE (0). These functions work for both numbers and strings. = Equal Not equal. Synonym: != = Bigger or equal > Bigger ISNULL(A) Returns 1 if A is NULL else 0. Same as ’( A == NULL ’). A BETWEEN B AND C A is bigger or equal as B and A is smaller or equal to C. Is the same as (A >= B AND A

String comparison functions. expr IN (value,...) Returns 1 if expr is any of the values in the IN list, else it returns 0. If all values are constants, then all values are evaluated according to the type of expr and sorted. The search for them item is then done by using a binary search. This means IN is very quick when used with constants in the IN part. expr LIKE expr SQL simple regular expression comparison. Returns TRUE (1) or FALSE (0). With LIKE you have two wild characters ’ stands for any number of characters, even zero characters. ’_’ stands exactly one character. If you want to search after a ’%’ or a ’_’ you must precede it with a ’\’ For example the string "Monty was here" is matched by "Monty " % Monty ___ h%" and "%was%".

expr NOT LIKE expr Returns TRUE (1) or FALSE (0). expr REGEXP expr Checks string against extended regular expr. expr NOT REGEXP expr Checks string against extended regular expr. STRCMP() Returns 0 if the strings are the same. Otherwise return -1 if first argument is smaller according to sort-order, otherwise it returns 1. Control flow functions. IFNULL(A,B) If A is not null it returns A, else B. IF(A,B,C) If A is true ( 0 and NULL) then return B, else return C. Mathematical functions. These returns NULL in the case of a error. - Sign ABS() SIGN() Sign of argument. Returns -1, 0 or 1. MOD() % Module (like in C).

Equivalent with MOD(). FLOOR() CEILING() ROUND() EXP() LOG() LOG10() POW() SQRT() PI() COS() SIN() 41

TAN() TAN2() ACOS() ASIN() ATAN() RAND([integer_expr]) Returns a random float, 0

SUBSTRING(A FROM B FOR C) Same as SUBSTRING(A,B,C). This is ANSI SQL 92. SUBSTRING(A FROM B) Same as RIGHT(A,B). This is ANSI SQL 92. SUBSTRING_INDEX(string,delimiter,count) Returns the substring from ’string’ after ’count’ delimiters. If count is positive the strings are searched from left else if count is negative the substrings are searched and returned from right. substring("www.tcx.se " , 2) would return "www.tcx" and substring("www.tcx.se , - 2) would return "tcx.se".

REPLACE(A,B,C) Replaces all occurrences of B in A with C. REPEAT(string,count) Repeats string count times. If count max_allowed_size returns NULL. INSERT(org,start,length,new) Replaces substring org[start...length] with new. First position in string=1. LCASE(A) Changes A to lower case. Synonym: LOWER() UCASE(A) Changes a to upper case. Synonym: UPPER() ENUM(A,a,b,c,d) Returns 1 if A == a, 2 if A == b. If no match 0 is returned. A,a,b,c,d... are strings. ELT(N,a,b,c,d,...) Returns a if N == 1, b if N == 2. a,b,c,d are strings. FIELD(A,a,b,c,d,...) Returns index of A in the a,b,c... list. The complement of ELT().

Date and time functions.

PERIOD_ADD(P:N) Adds N months to period P (of type YYMM or YYYYMM). Returns YYYYMM. PERIOD_DIFF(A,B) Returns months between periods A,B. A and B should be of format YYMM or YYYYMM. Example: PERIOD_DIFF(9612,199712). TO_DAYS(DATE) Changes a DATE to a daynumber. DATE may be a date string, a datetime string, a timestamp([6 | 8 | 14]) or a number of format YYMMDD or YYYYMMDD. FROM_DAYS() Changes a daynumber to a DATE. WEEKDAY(DATE) Gets weekday for date (0 = Monday, 1 = Tuesday). DATE may be a date string, a datetime string, a timestamp([6 | 8 | 14]) or a number of format YYMMDD or YYYYMMDD. CURDATE() Returns date of today.

In form YYYYMMDD or "YYYY-MM-DD" depending on whether CURDATE() is used in a number or string context. Synonymes: CURRENT_DATE(). CURTIME() Returns current time in form HHMMSS or "HH:MM:SS", depending on whether CURTIME() is used in a number or string context. Synonymes: CURRENT_TIME().

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NOW() Returns current time. In format YYYYMMDDHHMMSS or "YYYY-MM-DD HH:MM:SS" depending on whether NOW() is used in a number or string context. Synonymes: CURENT_TIMESTAMP(), SYSDATE(). UNIX_TIMESTAMP([DATE]) If called without any arguments a unix timestamp (seconds in GMT since 1970.01.01 00:00:00) is returned. Normally it is called with a timestamp column as an argument in which case it returns the timestamp. DATE may also be a date string, a datetime string, or a number of format YYMMDD or YYYMMDD in local time.

FROM_UNIXTIME(unix_timestamp) Returns a string of the timestamp in YYYY-MM-DD HH:MM:SS or YYYYMMDDHHMMSS format depending on context.

SEC_TO_TIME(seconds) Returns the hours, minutes and seconds of the argument in H:MM:SS or HMMSS format depending on context. Miscellaneous functions. DATABASE() Returns current database name. USER() Returns current user name. Synonymes: SESSION_USER() and SYSTEM_USER(). PASSWORD() Calculates a password string. This must be used to store a password in the ’user’ grant table. ENCRYPT(string[,salt]) Crypt messsage with the unix crypt() command. The salt should be a string with 2 characters. LAST_INSERT_ID() Returns the last automaticly generated value that was set in a auto_increment column. See section How can I get the unique ID for the last row? [p 83] FORMAT(nr,NUM) Formats number to a format like ’ with NUM decimals.

Functions for GROUP BY clause.

count(expr) Number of rows. count(*) is optimised to return very quickly if no other column is used in the SELECT. avg(expr) Average value of expr. min(expr) max(expr) Minimum/Maximum value of expr. min() and max() may take a string argument and will then return the minimum/maximum string value. sum(expr) Sum of expr. std(expr) Standard derivation of expression. This is a extension to ANSI SQL. bit_or(expr) The logical OR of all bits in expr. Caclulation done with 64 bits precision. 44

bit_and(expr) The logical AND of all bits in expr. Caclulation done with 64 bits precision.

MySQL has extended the use of GROUP BY. You can use columns or calculations in the SELECT expressions which doesn’t appear in the GROUP BY part. This stands for ’any possible value for this group’. By using this, one can get a higher performance by avoiding sorting and grouping on unnecessary items. For example, in the following query one doesn’t need to sort on b.name: SELECT a.id,b.name,COUNT(*) from a,b WHERE a.id=b.id GROUP BY a.id INSERT syntax INSERT INTO table [ (column_name ] VALUES (expression,...) or INSERT INTO table [ (column_name ] SELECT .... An expression may use any previous column in column_name list (or table if no column name list is given).

The following holds for a multi-row INSERT statement: The query cannot contain an ORDER BY clause. The target table of the INSERT statement cannot appear in the FROM clause of the query. If one uses INSERT INTO ... SELECT ... then one can get the following info string with the C API function mysql_info(). @result{Records: 100 Duplicates: 0 Warnings: 0} Duplicates are number of rows which couldn’t be written because some key would be duplicated. Warnings are columns which were set to NULL, but have been declared NOT NULL. These will be set to their default value.

If one sets a time stamp value to anything other than NULL, the time stamp value will be copied to the result table.

Auto increment fields works as usual. LOAD DATA INFILE syntax LOAD DATA INFILE ’table_interval.text’ [REPLACE | IGNORE] INTO TABLE table_interval [FIELDS [TERMINATED BY [ OPTIONALLY] ENCLOSED BY ’"’ ESCAPED BY [ LINES TERMINATED BY ’\n’] [(field list)] This is used to read rows from a text file, located on the server, at a very high speed. The server-client protocol doesn’t yet support files over a connection. If you only have the file on the client, use rcp or ftp to copy it, possibly compressed, to the server before using LOAD DATA INFILE. To write data to a text file, use the SELECT ...

INTO OUTFILE ’interval.txt’ fields terminated by ’,’ enclosed by ’"’ escaped by ’ lines terminated by ’\n’ FROM . syntax.

Normally you don’t have to specify any of the text file type options. The default is a compact text file with columns separated with tab characters and all rows end with a newline. Tabs, newlines and \ inside fields are prefixed with a \. NULL’s are read and written as \N. 45

FIELDS TERMINATED BY has the default value of \t. FIELDS [OPTIONALLY] ENCLOSED BY has the default value of ". FIELDS ESCAPED BY has the default value of ’ . LINES TERMINATED BY has the default value of ’\n’. FIELDS TERMINATED BY and LINES TERMINATED BY may be more than 1 character.

If LINES TERMINATED BY is an empty string and FIELDS TERMINATED BY is not empty then lines are also terminated with FIELDS TERMINATED BY. If FIELDS TERMINATED BY and FIELDS ENCLOSED BY both are empty strings (") then this gives a fixed row format ("not delimited" import format). With a fixed row size NULL values are outputed as a blank string. If you specify OPTIONALLY in ENCLOSED BY, then only strings are enclosed in ENCLOSED BY by the SELECT ... INTO statement.

Duplicated ENCLOSED BY chars are removed from strings that start with ENCLOSED BY. For example: With ENCLOSED BY ’"’: "The ""BIG"" boss" -> The "BIG" boss The "BIG" boss -> The "BIG" boss If ESCAPED BY is not empty then the following characters will be prefixed with the escape character: ESCAPED BY, ASCII 0, and the first character in any of FIELDS TERMINATED BY, FIELDS ENCLOSED BY and LINES TERMINATED BY. If FIELDS ENCLOSED BY is not empty then NULL is read as a NULL value. If FIELDS ESCAPED BY is not empty then \N is also read as a NULL value.

If REPLACE is used, then the new row will replace all rows which have the same unique key.

If IGNORE is used, the row will then be skipped if there already exist a record with an identical unique key. If none of the above options are used an error will be issued. The rest of the text file will be ignored if one gets a duplicate key error. Some possible cases that’s not supported by LOAD DATA: Fixed size rows (FIELDS TERMINATED BY and FIELDS ENCLOSED BY both are empty) and BLOB fields. If some of the separators are a prefix of another. FIELDS ESCAPED BY is empty and the data contains LINES TERMINATED BY or FIELDS ENCLOSED BY followed by FIELDS TERMINATED BY.

All rows are read into the table. If a row has too few fields the rest of the fields are set to default values. For security reasons the text file must either reside in the database directory or be readable by all. For more information about the escaped syntax See section Literals. How do you write strings and numbers? [p 30] . 46

When the LOAD DATA query is done, one can get the following info string with the C API function mysql_info(). @result{Records: 1 Deleted: 0 Skipped: 0 Warnings: 0} Warnings are incremented for each column which can’t be stored without loss of precision, for each column which didn’t get a value from the read text line (happens if the line is too short) and for each line which has more data than can fit into the given columns.

Example that loads all fields; LOAD DATA INFILE ’persondata.text’ INTO TABLE persondata; See section How should I arrange my table to be as fast/small as possible? [p 59] UPDATE syntax UPDATE table SET column=expression,... WHERE where_definition All updates are done from left to right. If one accesses a column in the expression update will then use the current value (a given value or the default value) of the column.

UPDATE persondata SET count=count+1 SHOW syntax. Get information about names of columns. SHOW DATABASES [LIKE wild] or SHOW TABLES [FROM database] [LIKE wild] or SHOW COLUMNS FROM table [FROM database] [LIKE wild] Gives information about databases, tables or columns. The wild is a LIKE string. FIELDS may be used as an alias for COLUMNS. EXPLAIN syntax. Get information about a SELECT. EXPLAIN SELECT select_options Gives information about how and in which order tables are joined. With the help of EXPLAIN one can see when one has to add more keys to tables to get a faster select that uses keys to find the records.

You can also see if the optimiser joins the tables in an optimal order. One can force the optimiser to use a specific join order with the STRAIGHT_JOIN option to select.

The different join types are: system The table has only 1 record (= system table) const The table has at most 1 matching record which will be read at the start of the query. All columns in this table will be regarded as constants by the rest of the optimiser. eq_ref One record will be read from this table for each combination of the previous tables. 47

ref All records with matching keys will be read from this table for each combination of the previous tables. all A full table scan will be done for each combination of the previous tables. DESCRIBE syntax.

Get information about columns. (DESCRIBE | DESC) table [column] Gives information about columns. This command is for Oracle compatibility. See section SHOW syntax. Get information about names of columns. [p 47] Column may be a column name or a string. Strings may contain wild cards. Lock tables syntax LOCK TABLES table_name [AS alias] READ|WRITE [, table_name READ|WRITE . . UNLOCK TABLES Locks tables for this thread. Many threads may have a READ lock on the same table, but one can use a table with a WRITE lock. One can’t update a table on which one has a read LOCK. When one uses LOCK TABLES one must lock all tables one is going to use!

LOCK TABLES t READ, t as t2 READ SELECT * from t,t2; All tables are automaticly unlocked when one issues another LOCK TABLES or if the connection to the server is closed. SET OPTION syntax. SET OPTION SQL_VALUE_OPTION=value, ... The used options remain in effect for the whole current session. The different options are: SQL_SELECT_LIMIT=value The maximum number of records to return in any select. If a select has a limit clause it overrides this statement. The default value for a new connection is ’unlimited’. SQL_BIG_TABLES= 0 | 1 If set to 1 then all temporary tables are stored on disk based.

This will be a little slower, but one will not get the error The table ### is full anymore for big selects that require big temporary tables. The default value for a new connection is 0 (use in memory temporary tables). SQL_BIG_SELECTS= 0 | 1 If set to 1 then MySQL will aborts if one will try to make a select with probably will take a very long time. This is nice to SELECTS with a wrong WHERE statement. A big query is defined as a SELECT that will probably have to examine more than max_join_size rows. The default value for a new connection is 0 (allow all SELECT’s). 48

GRANT syntax. (Compatibility function). GRANT (ALL PRIVILEGES | (SELECT, INSERT, UPDATE, DELETE, REFERENCES (column list), USAGE)) ON table TO user [ WITH GRANT OPTION] This command doesn’t do anything. It is only in MySQL for compatibility reasons. Privileges in MySQL is handled with the mysql grant tables. See section How does the privilege system work? [p 26] CREATE INDEX syntax (Compatibility function). CREATE [UNIQUE] INDEX index_name ON table_name ( column_name ) This function doesn’t do anything. It is only in MySQL for compatibility reasons. You can create new index with ALTER TABLE.

See section ALTER TABLE syntax [p 37] DROP INDEX syntax (Compatibility function). DROP INDEX index_name This always succeeds. You can drop an index with ALTER TABLE. See section ALTER TABLE syntax [p 37] Is MySQL picky about reserved words? It seems that I can’t create a table with column names timestamp or group. Functions don’t clash with table or column names. (For example ABS is an allowed column name). The only restriction is that space is not allowed between a function name and the ’(’ when using functions.

The following are reserved words in MySQL. Most of them (for example) group, are forbidden by ANSI SQL92 as column and/or table names. A few are because MySQL needs them and is (currently) using a Yacc parser: 49

action add all alter and as asc auto_increment between bigint bit binary blob both by cascade char character change check column columns create data databases date datetime dec decimal default delete desc describe distinct double drop escaped enclosed enum explain fields float float4 float8 foreign from for full grant group having ignore in index infile insert int integer interval int1 int2 int3 int4 int8 into is key keys leading like lines limit lock load long longblob longtext match mediumblob mediumtext mediumint middleint numeric no not null on option optionally or order outfile partial precision primary procedure privileges read real references regexp repeat replace restrict rlike select set show smallint sql_big_tables sql_big_selects sql_select_limit straight_join table tables terminated text time timestamp tinyblob tinytext tinyint trailing to unique unlock unsigned update usage values varchar varying with write where zerofill The following symbols (from the table above) are disallowed by ANSI SQL but allowed by MySQL as column/table names.

This is because some of theese names are very natural names so a lot of people has already used them.

ACTION BIT DATE 50

ENUM NO TEXT TIME TIMESTAMP Go to the first [p 5] , previous [p 26] , next [p 52] , last [p 87] section, table of contents [p 1] . 51

Go to the first [p 5] , previous [p 30] , next [p 57] , last [p 87] section, table of contents [p 1] . How safe/stable is MySQL How stable is MySQL? At TcX, MySQL has worked without any problems in our projects since nid 1996. When released to a wider public we noticed that there where some parts of ’untested code’ in MySQL that was quickly found by the new user group that don’t do queries exactly like we do at TcX.

Each new release have had fewer non portability problems than the previous one, even though they have had a lot of new features, and we hope that one of the next releases will be possible to be labelled ’stable’. Each release of MySQL has been usable and there has only been problems when users start to use code from ’the gray zones’. Naturally, outdoor users can’t know what the gray zones are and I hope this section will clarify those currently known.

We will here try to answer some of the more important questions that seems to concern a lot of people and clarify some issues. This section has been put together from the information that has come forward in the mailing list which is very active in reporting bugs. How stable is MySQL? Can I depend on MySQL in this project! This is about the 3.21.x version of MySQL. All known and reported bugs are fixed in the latest version with the exception of the bugs listed in the BUGS file which are things that are ’design’ related.

MySQL is written in multiple layers and different independent modules.

Here is a list of the different modules and how tested each of them are. The ISAM table handler. Stable (ISAM) where all data is stored. In all MySQL releases there hasn’t been a single (reported) bug in this code. The only known way to get a corrupted table is to kill the server in the middle of a update and because all data is flushed to disk between each query even this is unlikely to destroy any data beyond rescue. There hasn’t been a single bug report about lost data because of bugs in MySQL either.

The parser and lexical analyser. Stable There hasn’t been a single reported bug in this system for a couple of months. The C client code. Stable No known problems. In early 3.20 releases there were some limitations in the send/receive buffer size. In 3.21.x the send/receive buffer is now dynamic up to a default of 512K. mysql, mysqladmin and mysqlshow. Stable The command line clients have had very few bugs. mysqldump and mysqlimport. Beta Rewritten for 3.21. Basic SQL. Stable The basic SQL function system and string classes and dynamic memory handling. Not a single reported bug on this system.

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Query optimiser. Gamma Some changes in 3.21. Range optimiser. Alpha Totally rewritten for 3.21.x Join optimiser. Gamma Small changes for 3.21. GROUP BY, ORDER BY and related function COUNT(). Beta Rewritten for 3.21 and throughly tested. Locking. Gamma This is very system dependent. One some system there is big problems to use standard OS locking (fcntl). In these case one should run the MySQL demon with the --skip-locking flag. Known problems are some Linux systems and SUNOS when using NFS mounted file systems. Linux threads. Gamma The only found problem is with the fcntl() call, which is fixed by using --skip-locking.

Some people have reported lockup problems with the 0.5 release.

Solaris 2.5+ pthreads. Stable We use this for all our production work. MIT threads (Other systems). Beta No reported bugs since 3.20.15 and no known bugs since 3.20.16. On some system there is ’misfeature’ where some operations are quote slow (a 1/20 second sleep is done between each query). Other thread implementions. Alpha The ports to other systems is very new and may still have bugs, either in MySQL or most often in the thread implementation itself. LOAD DATA..., INSERT ... SELECT. Stable Some people have thought they have found bugs in this but has turned up being misunderstandings. So check the manual before reporting bugs! ALTER TABLE.

Gamma Partly rewritten for 3.21. mysqlperl. Stable No bugs reported except a lot of compiling and linking problems. DBD. Beta Now maintained by Jochen Wiedmann . Thanks! mysqlaccess. Beta Written and maintained by Yves.Carlier@rug.ac.be. Thanks! The Technical Documentation. Beta It is improving.

MyODBC (uses ODBC SDK 2.5). Beta It seams to work well with some programs. There is some known problems with Office97. PowerBuilder doesn’t work yet. Error messages aren’t returned right when using a Microsoft New ODBC 3.0 driver but this may well be a bug in the Microsoft ODBC 3.0 driver. It isn’t fully up to ODBC level 2 yet in every regard. (My personal opinion is that the ODBC levels are defined in such a way that it’s almost impossible to make a simple ODBC driver that works with all products). Sometimes the MyODBC code must be ported to ODBC 3.0.

TcX provides email support for paying customers, but the MySQL mailing list usually provides answers to all common questions.

Bugs are usually fixed right away with a patch that usually works and for serious bugs there is almost always a new release. 53

Why are there is so many release of MySQL? Is it because there are so many bugs? Well, MySQL is evolving quite rapidly here at TcX and we want to share this with other MySQL users. We try to make a release when we have a very useful feature that others seem to have a need for. We also try to help out users who request features that are easy to implement. We also take note on what our licensed users want to have and we especially take notes on what our extended email supported customers want and try to help them out.

No one has to download a new release. The NEWS file will tell you if the new release has something you really want.

If there is, by any chance, a fatal bug in a release we will make a new release as soon as possible, that fixes the problem. We would like other companies to do this too :) The 3.21.x version has had many big changes for portability to a lot of different systems. When the 3.21 release is stable we will remove the alpha/beta suffix and move active development to the 3.22. Bugs will still be fixed in the stable version. We don’t believe in a complete freeze, as this also leaves out bug fixes and things that ’must be done’. ’Somewhat freezed’ means that we will maybe add small things that ’almost surely will not affect anything thats already working’.

Checking a table for errors.

If MySQL crashed (for example if the computer is turned off) when all data is not written to disk the tables may have become corrupted. To check a table use: isamchk table_name This finds 99.99 % of all errors. What it can’t find is when only the data file has been corrupted. isamchk -e table_name This goes through all data and does a complete check. isamchk -ei table_name As the above but it also prints some statistics. We at TcX run a cron job on all our important tables once a week. 35 0 * * 0 /path/to/isamchk -s /path/to/dbs/*/*.ISM This prints out any crashed tables so we can go and examine and repair them when needed.

As we haven’t had any unexpected crashed (without hardware trouble) tables for a couple of years now (this is really true), once a week is more than enough of us.

Of course, whenever the machine has done a reboot in the middle of a update one usually has to check all the tables that could have been affected. (This is a ’expected crashed table’) We recommend that to start with one should do a isamchk -s on all updated tables each night until one gets to trust MySQL as much as we trust it. 54

Naturally, one could add a check to safe_mysql that, if there is an old pid file left after a reboot, it should check all tables that have been modified the last 24 hours. How to repair tables. The file format that MySQL uses to store data has been extensively tested, but there is always instances (like a hard kill on the mysqld process in the middle of a write, a hardware error or a unexpected shutdown of the computer) when some tables may be corrupted.

The sign of a corrupted table is usually when queries abort unexpectedly and one gets errors like: table.frm is locked against change.

Can’t find file ’table.ISM’ (Errcode # ) Got error ### from table handler. (Error 135 is an exception in this case) Unexpected end of file. Record file is crashed. In thess cases you have to repair your tables. The isamchk extern utility can usually detect and fix most things that can go wrong. See section The MySQL table check, optimize and repair program [p 66] . If you are going to use isamchk on very large files, you should first decide how much memory you want to give to isamchk. More memory gives more speed. For example, if you have more than 32M ram, try: isamchk -O sortbuffer=16M -O keybuffer=16M -O readbuffer=1M -O writebuffer=1M .

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Part 1; Checking Check the permissions of the table files. Make them readable for the user running mysqld. cd to the database directory. Run ’isamchk *.ISM’ or (’isamchk -e *.ISM’ if you have more time). You only have to repair those tables that your isamchk gives an error. Use option -s to avoid unnecessary information. Part 2; Easy safe repair. If you get weird errors when checking or repairing, like out of memory or if isamchk crashes, go to part 3. Try first ’isamchk -rq table’. This will try to repair the .ISM file without touching the important data table (.ISD). If the data file (.ISD) contains everything and the delete links point at the right places in the data file, this should work and the table is fixed.

Start repairing next table.

Make a backup of the data file (table.ISD) before continuing. Use ’isamchk -r table’. This will remove wrong records and deleted records from the data file and reconstruct the index (.ISM) file. If the above fails, use ’isamchk -ro table’. This is a little slower but a crash-safer version of the above. Part 3; Hard repair. This should only happen if the first 16K block in the .ISM file is destroyed, contains wrong information or if the .ISM is missing. In this case we have to create a new .ISM file. Do as follows: 55

Move the data file .ISD file to some safe place.

Recreate the .ISM file from the .frm file: shell> mysql database mysql> delete from table_name; mysql> quite Copy (don’t move) the data file (.ISD) back on the newly created .ISD file Go back to Part 2. (This shouldn’t be a endless loop). isamchk -rq should now work. Part 4; Very hard repair. This can only happen if the descriptor file (.frm) also has crashed. This should never happen, because the .frm file isn’t written to after the table is created. Restore the .frm file from a backup and go back to Part 3. You can also restore the .ISM file and go back to Part 2. In the latter case you should start with ’isamchk -r’.

If you don’t have a backup but know exactly how the table was created, create a copy of the table in another database and copy the .frm and .ISM file from there to your crashed database and go back to Part 2; Is there anything special to do when upgrading/downgrading MySQL?

One can always move the MySQL form and data files between different versions on the same architecture as long as one has the same base version of MySQL. The current base version is of course 3. If one changes the sort order by recompiling MySQL one has to do a isamchk -rq on the tables. Go to the first [p 5] , previous [p 30] , next [p 57] , last [p 87] section, table of contents [p 1] . 56

Go to the first [p 5] , previous [p 52] , next [p 65] , last [p 87] section, table of contents [p 1] . How to get maximum performance out of MySQL How does MySQL use memory ? You can get the currently used buffer sizes with: > ./mysqld --help This should result in a list of all mysqld options and configurable variables like the following.

See section How can I change the buffer sizes of mysqld ? [p 61] . Possibly variables to option --set-variable (-O) are: back_log current value: 5 join_buffer current value: 131072 key_buffer current value: 1048568 max_allowed_packet current value: 65536 max_connections current value: 90 max_join_size current value: 4294967295 max_sort_length current value: 1024 net_buffer current value: 8192 record_buffer current value: 131072 table_cache current value: 64 tmp_table_size current value: 131072 sort_buffer current value: 2097144 All threads share the same base memory. Nothing is memmaped yet (except compressed tables but that’s another story).

This is because 32bit memory space of 4GB is not large enough for most large tables. When we get a system with 64 bit address space we may add general support for memmaping. When starting mysqld one can specify a key buffer. This will buffer all keys in all tables at FIFO basis (variable keybuffer).

Each connection uses some thread space, a stack and a connection buffer (variable net_buffer_length). Each request doing a sequential scan over a table allocates a read buffer (variable record_buffer). Each request doing a sort, allocates a sortbuffer and one or two temporary files. The maximum extra disk-space needed is @math{(sort_key_length +sizeof(long))*2}. All joins are done in one pass and most temporary tables are memory based (HEAP) tables. Temporary tables with a big recordlength (= sum of all column length) or that contains BLOB’s are stored on disk. One current problem is that if the HEAP table exceeds the size of tmp_table_size, one will get the error: ’The table ### is full’.

In the future we will fix this by automatically changing the in memory (HEAP) table to a disk based (NISAM) table if needed. To go around this problem one can increase the -O tmp_table_size=# option to mysqld or use the SQL option SQL_BIG_TABLES. See section SET OPTION syntax. [p 48] . In MySQL 3.20 the maximum size of the temporary table was recordbuffer*16, so if you are using this version you have to increase recordbuffer. There also exists a patch to always store temporary tables on disk, but this will affect the speed of all complicated queries. Almost all memory used when parsing and calculating is done on a local memory store.

No memory overhead is needed for small items and the normal slow memory allocation/freeing is avoided. Memory is only allocated for unexpectedly large strings (this is done with malloc/free). 57

Each index file is opened once and the data file is opened once for each concurrently running thread. For each concurrent thread a table structure, column structures for each column and a buffer that has the size of 3 * (maximum row length not counting BLOBS) is allocated. A BLOB uses 5 to 8 bytes +length of blob data. For each table having BLOBS, a buffer is enlarged dynamically to read in larger BLOB’s. If one scans a table there will be a allocated buffer as large as the largest BLOB. All used tables are saved in a cache and used by FIFO. Normally the cache is 64 tables. If a table has been used by 2 running threads at the same time, there will be 2 entries of the table in the cache.

A MySQLadmin refresh closes all tables that are not used and marks all used tables to be closed when the running thread finishes. This will effectively free most used memory. When running mysqld ps, other programs may report that is takes a lot of memory. This may be caused by thread-stacks on different memory addresses. For example, the Solaris ps calculates the unused memory between stacks as used memory. You can verify this by checking available swap with ’swap -s’. We have tested mysqld with commercial memory-leakage detectors so there should not be any memory leaks.

How does MySQL use keys? All keys, PRIMARY, UNIQUE and INDEX(), are stored in B trees.

Strings are automatically prefix- and end-space compressed. INDEX(col1, col2) creates a multiple index over the two columns. The key can be seen like a concatenation of the given columns. If you use INDEX(col1), INDEX(col2) instead of INDEX(col1,col2) you get two separate keys instead. SELECT * FROM table WHERE col1=# AND col2=# In a case of INDEX(col1,col2) the right row(s) can be fetched directly. In a case of INDEX(col1), INDEX(col2) the optimiser decides which index will find fewer rows and this index will be used to fetch the rows.

If the table has an index INDEX(col1,col2,col3 ) the prefix of this can be used by the optimiser to find the rows. This means that the above gives you search capabilities on: INDEX(col1) and INDEX(col1,col2) and INDEX(col1,col2,col3)... MySQL can’t use a sub part of a key to locate rows through a key. With the definition INDEX(col1,col2,col3): SELECT * FROM table WHERE col1=# SELECT * FROM table WHERE col2=# SELECT * FROM table WHERE col2=# and col3=# only the first query will use keys. 58

How does MySQL open & close tables? The cache of open tables can grow to a maximum of table-cache (default 64, changeable with -O table_cache=#).

A table is never closed, except when the cache is full and another thread tries to open a table or if one uses ’mysqladmin refresh’. When the limit is reached, MySQL closes as many tables as possible, until the cache size has been reached or there are no more unused tables. This means that if all tables are in use by some threads, there will be more open tables than the cache limit, but the extra tables will be closed eventually. Tables are closed according to last-used order.

A table is opened (again) for each concurrent access. This means that if one has two threads running on the same table or access the table twice in the same query (with AS) the table needs to be opened twice. The first open of any table takes 2 file descriptors, each following use of the table takes only one file descriptor. How should I arrange my table to be as fast/small as possible? Use NOT NULL if possible. It makes everything faster and you save 1 bit per column. All columns have default values. Only insert when the default value isn’t acceptable. You don’t have to insert the columns of a timestamp or an autoincremented key in the insert statement.

See section How can I get the unique ID for the last row? [p 83] Use the smaller INT types if possible to get smaller tables. For example, MEDIUMINT is often better than INT.

If you don’t have any VARCHAR columns, a fixed size record format will be used. This is much faster but may unfortunately waste some space. See section What are the different row formats? Or when to use VARCHAR/CHAR? [p 63] . To make MySQL optimise queries better, run isamchk -a on the table once it is loaded with relevant data. This updates a value for each index that tells how many rows that have the same value for this key in average. Of course, this is always 1 for unique indexes. To sort an index and data according to an index use isamchk -Sir1 (if you want so sort on index 1). If you have a unique key that you want to read all records from in numeric order this is a good way to make that faster.

When loading a table with data use LOAD DATA FROM INFILE. This is usually 20 times faster than using a lot of INSERTs. If the text file isn’t on the server, rcp it to the server first. See section LOAD DATA INFILE syntax [p 45] . You can even get more speed when loading data to tables with many keys by doing: Create the table in mysql or perl with CREATE TABLE.... Do a mysqladmin refresh. Use isamchk -k0 database/table_name. This will remove all use of keys from the table. Insert data into the table with LOAD DATA INFILE.... If you have pack_isam and want to compress the table, run pack_isam on it.

Recreate the keys with isamchk -rq database/table_name. Do mysqladmin refresh.

The other possibility to get some more speed to both LOAD DATA FROM INFILE and INSERT is to enlarge the key buffer. This can be done with the -O key_buffer=# option to (safe)mysqld. For example 16M should be a good value if you have much RAM :) When dumping data as textfiles to other programs, use SELECT ... INTO OUTFILE. See 59

section LOAD DATA INFILE syntax [p 45] . When doing many inserts/updates in a row, you can get more speed by using LOCK TABLES on the tables. ...FROM INFILE... and ...INTO OUTFILE... are atomic so you don’t have to use LOCK TABLES when using these.

See section Lock tables syntax [p 48] . To check how you are doing, run isamchk -evi on the .ISM file. What affects the speed of the INSERT statement? The time to insert a record consists of: Connect: (3) Sending query to server: (2) Parsing query: (2) Inserting record: (1 x size of record) Inserting keys: (1 x keys) Close: (1) Where (number) is proportional time. This does not take into calculation the initial overhead to open tables (which is done once for each simultaneous running query).

The size of the table slows down the insert of keys with N log N (B-trees). What affects the speed of DELETE statement? The delete time of a record is exactly proportional to the number of keys. To increase the seed of deletes you can increase the size of the key cache. The default key cache is 1M and to get faster deletes it should be increased a couple of times (try 16M if you have enough memory). What kind of optimisation is done on the WHERE clause? (Incomplete, MySQL does a lot of optimisations.) Brace removal (all unnecessary braces are removed). ((a AND b) AND c OR (((a AND b) AND (c AND d ( a AND b) OR (a AND b AND c AND d) Constant folding.

(a b>5 AND b=c A=5 Constant condition removal (needed because of constant folding). (b>=5 AND b=5) OR (b=6 and 5=5) or (B=7 and 5=6) -> B=5 or B=6 All constant expressions used by keys are evaluated only once. Return zero rows if impossible select.

HAVING is merged with WHERE if one doesn’t use GROUP BY or group functions. For each sub join a simpler WHERE is constructed to get a fast WHERE evaluation for each sub join and also to skip records as soon as possible. Find all keys that may be used. Use the key which finds least records. A key is used for the following cases = ,

key = 1 or A = 10 and key=2 -> key = 1 OR key = 2 key_part_1 = const and key_part_3 = const -> key_part_1 = const Read all constant tables. A constant table is: 1. A table with 0 or 1 record. 2. A table which uses only other const tables and constants on a full unique key.

const_table.key = constant const_table.key_part_1 = const_table2.column and const_table.key_part_2 = constant Find the best join combination to join the tables, by trying all possibilities :(. If all columns in ORDER BY and in GROUP comes from the same table, then this table is preferred first when joining.

If there is a order clause and a different group clause or if the order or group contains columns from other tables than the first table in the join cue, a temporary table is created. For each table use a ranged key, if possible, to read records. Each table index is queried and if there exists a key range that spans < 30% of the records then a key is used. If no such key can be found a quick table scan is used. Before each record is output-ed, skip those that match the HAVING clause. How can I change the buffer sizes of mysqld ?

With the mysqld -O variable=size command. Example run: > mysqld --help (or > mysqld -?) >mysqld --help /my/monty/sql/mysqld Ver 3.21.0-alpa for SOLARIS 2.5 (SPARCstation) TcX Datakonsult AB, by Monty.

This is FPL, not free software This software comes with NO WARRANTY: see the file PUBLIC for details. Starts the mysql server Usage: /my/monty/sql/mysqld [OPTIONS] -b, --basedir=path path to installation directory -h, --datadir=path path to the database root - - debug=... output debug log. Often this is ’d:t:o,filename‘ -T, --debug-info print some debug info at exit - - help display this help and exit -L, --language=... client error messages in given language -l, --log[=filename] log connections and queries to file --log-update[=filename] log updates to filename.# where # is a unique number if not given.

--log-isam[=filename] log all isam changes to file -P, --port=... Port number to use for connection -O, --set-variable var=option give a variable an value. --help lists variables --skip-new-routines don’t use new possible wrong routines. --skip-grant-tables start without grant tables. This gives anyone FULL ACCESS to all tables! --skip-locking don’t use system locking. To use isamchk one has to shut down the server. --skip-name-resolve Don’t resolve hostnames. All hostnames are IP’s or ’localhost’ --skip-new-routines don’t use new possible wrong routines. --skip-unsafe-select skip unsafe select optimisations.

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--socket=... Socket file to use for connection -V, --version output version information and exit Current base_dir: /my/monty Current data_dir: data/ Current language: english/ Possibly variables to option --set-variable (-O) are: back_log current value: 5 join_buffer current value: 131072 key_buffer current value: 1048568 max_allowed_packet current value: 65536 max_connections current value: 90 max_join_size current value: 4294967295 max_sort_length current value: 1024 net_buffer current value: 8192 record_buffer current value: 131072 table_cache current value: 64 tmp_table_size current value: 131072 sort_buffer current value: 2097144 > safe_mysqld -O key_buffer=512k -O sort_buffer=100k -O record_buffer=100k & The key_buffer is shared by all threads, the rest are allocated when needed.

mysqld demon starts with a cd to ’mysql-data-dir’. After this, mysqld-data-dir is changed to ’./’ (current dir). All paths (databases, pid file, and log file) are prefixed with ’ . What options to use to get MySQL to run at full speed?

More memory gives more speed. You can try something like: mysqld -O key_buffer=16m -O sort_buffer=1m -O record_buffer=512k --skip-locking --skip-locking disables file locking between SQL requests. If this is used then the following can happen: If mysqld or the machine crashes a table has a higher risk of being corrupted. Tables should at least be checked with isamchk *.ISM after a crash. One MUST flush all tables with mysqladmin refresh before one tries to check/repair tables with isamchk. (isamchk -d table_name is always allowed).

The --skip-locking is default when compiling with MIT threads.

This is because flock() isn’t fully support by MIT threads on all platforms. How to get MySQL to run as fast as possible with little memory? If there are very many connections, ’swapping problems’ may occur, unless mysqld hasn’t been configured to use very little memory for each connection. 62

For example, for 200 open connections one should have a table cache of at least 200 * (max_number of tables in join). Of course MIT threads may slow down everything a bit, but for key based selects a select is usually down in one time frame so there shouldn’t be a mutex locking/thread juggling. If updates are a problem, updates can be delayed and then do many updates in a row later. Many updates done in a row are much quicker than one at a time. If the problem is with MIT threads and one is using FreeBSD x.x. upgrading to FreeBSD 3.0.(or higher:) should help. This gives a possibility to use sockets (quicker than the current TCP/IP with MIT threads) and the thread package is much more integrated.

What are the different row formats? Or when to use VARCHAR/CHAR? Actually using no VARCHAR or BLOB types results in a fixed row size. Otherwise CHAR and VARCHAR are the same. You can check the format used in a table with isamchk -d. MySQL has three different table formats: 1. Fixed length tables; This is the default format. All non packed columns are space filled. Very quick. Easy to cash. Easy to reconstruct if crashed, of course, this only theoretical :-) as records are in fixed positions. Don’t have to be reorganised unless a huge number of records are deleted. 2. Dynamic tables Is used if there exists any VARCHAR, TEXT or BLOB columns in a table.

All strings are dynamic (except if length < 3). Each record is preceded with a bitmap for which columns are not empty (this isn’t the same as null columns).

Each string is saved with a length byte + string. If string is zero length or a number is zero it takes no extra space, just the zero length bit for each column. Each record is uses the exact record space required. If a record becomes larger it is split into as many pieces as required. Takes little disk space. If records are changed a lot, isamchk -r should be run now and then to reorganise the table. This is to get a better layout. Use isamchk -ei table_name for some statistics. Not as easy to reconstruct because a record may be in many pieces and a link may be missing.

The expected row length for dynamic sized records is: 3 + (number_of_columns + 7) / 8 + (number of char columns) + packed_size_of_number_columns + length_of_strings + (null_columns + 7) / 8.

There will be a penalty of 6 bytes for each link. A dynamic record will be linked whenever a update causes a enlargement of the record. Each new link will be 63

at least 20 bytes, so the next enlargement will probably go in the same link. If not, there will be another link. You may check how many links there are with isamchk -ed. All links may be removed with isamchk -r. 3. Compressed tables (this is only with UNIREG/pack_isam) Read only tables. Takes very little disk space. Minimises disk usage. Each record is compressed separately (very little access overhead). Can handle fixed or dynamic length records, but no BLOBs. Can be uncompressed with isamchk. Why so many open tables? When you run mysqladmin status you get something like: Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12 This can be somewhat perplexing if you only have 6 tables.

As MySQL is multithreaded it may have many queries on the same table at once. To minimise the problem with two threads having different states on the same file, I open the table again for each concurrent thread. This takes some memory and one extra file descriptor for the data file. The index file descriptor is shared all threads.

Go to the first [p 5] , previous [p 52] , next [p 65] , last [p 87] section, table of contents [p 1] . 64

Go to the first [p 5] , previous [p 57] , next [p 75] , last [p 87] section, table of contents [p 1] . MySQL Utilites Overview of the different MySQL programs All MySQL client that communicates with the server uses the following environment variables: Name Description MYSQL_UNIX_PORT The default socket. Used with ’localhost’. MYSQL_TCP_PORT The default TCP port. MYSQL_PWD The default password. mysql A SQL shell (with gnu readline). Supports interactive use or as a non interactive query tool.

When used interactively result is given in a ascii-table format, but when used as a filter the result is a tab-separated output.

mysqlaccess Script to check the privileges for a host, user and database combination. mysqladmin Administration utility. Create/Drop of databases, reload (read new users) and refresh (flush tables to disk, reopen log files). Also gives version and process info. mysqld The SQL daemon. This should always be running. mysqldump Dump a MySQL database into a file with SQL statements or tab separated text files. Enchanted freeware originally by Igor Romanenko. mysqlimport Imports text-file(s) into respective table(s). Can use all formats supported by LOAD DATA INFILE. See section LOAD DATA INFILE syntax [p 45] mysqlshow Shows information about database, tables, fields and keys.

mysqlbug This script should always be used when filing a bug report to the MySQL list. mysql_install_db Creates the MySQL grant tables with default privileges. This is usually only executed when installing the first MySQL release on a new system.

isamchk Check, optimise and repair MySQL tables. make_binary_release Makes a binary release of a compiled MySQL. This could be sent by ftp to www.tcx.se/pub/mysql/Incoming for the convenience of other MySQL users. msql2mysql A shell script to convert a mSQL program to MySQL. Doesn’t handle all cases but gives a good start when converting. 65

replace Binary used for msql2mysql. Utility program to change strings in place in files or on stdin. Uses a finite state machine to match longer strings first. Can be used to swap strings, for example ’replace a b b a -- files’ swaps ’a’ and ’b’ in the given files.

safe_mysqld Starts the mysqld demon with some safety features. Restarts on error and has logging of runtime information to a log file. The MySQL table check, optimize and repair program For infromation about how to use isamchk to repair a crached table: See section How to repair tables. [p 55] .

Getting low level table information To get a description/statistics from a table use the forms below. We will explain some of the information in more detail later. isamchk -d table_name isamchk in ’describe mode’. If one uses ’--skip-locking’ isamchk may report an error for a table that is updated while isamchk runs, but there isn’t any risk of destroying data. A short form. ISAM file: company.ISM Data records: 1403698 Deleted blocks: 0 Recordlength: 226 Record format: Fixed length table description: Key Start Len Index Type 1 2 8 unique double 2 15 10 multip. text packed stripped 3 219 8 multip.

double 4 63 10 multip. text packed stripped 5 167 2 multip. unsigned short 6 177 4 multip. unsigned long 7 155 4 multip. text 8 138 4 multip. unsigned long 9 177 4 multip. unsigned long 193 1 text For explanations see below. isamchk -d -v table_name A little more verbose. ISAM file: company.ISM Isam-version: 2 Creation time: 1996-08-28 11:44:22 Recover time: 1997-01-12 18:35:29 Data records: 1403698 Deleted blocks: 0 Datafile: Parts: 1403698 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 3 Max datafile length: 3791650815 Max keyfile length: 4294967294 Recordlength: 226 Record format: Fixed length r table description: 66

Key Start Len Index Type Root Blocksize Rec/key 1 2 8 unique double 15845376 1024 1 2 15 10 multip. text packed stripped 25062400 1024 2 3 219 8 multip. double 40907776 1024 73 4 63 10 multip. text packed stripped 48097280 1024 5 5 167 2 multip. unsigned short 55200768 1024 4840 6 177 4 multip. unsigned long 65145856 1024 1346 7 155 4 multip. text 75090944 1024 4995 8 138 4 multip. unsigned long 85036032 1024 87 9 177 4 multip. unsigned long 96481280 1024 178 193 1 text ISAM file Name of isam file. Isam-version Version of isam format. Currently always 2. Creation time When was the data file created.

Recover time When was the index/data file last reconstructed. Data records How many records/rows. Deleted blocks How many deleted blocks still have reserved space. See section How to repair tables. [p 55] .

Datafile: Parts For dynamic record format this shows how many data blocks there are. For a optimised table without splits this is the same as Data records. Deleted data How many bytes of non reclaimed deleted data. Datafile pointer How many bytes the datafile pointer has. It is usually 2, 3 or 4 bytes. Most tables manage with 2 bytes but this cannot be controlled from MySQL yet. For fixed tables this is a record address. For dynamic tables this is a byte address. Keyfile pointer How many bytes has the datafile pointer. It is usually 1, 2 or 3 bytes. Most tables manage with 2 bytes but this is calculated automatically by MySQL.

It is always a block address. Max datafile length How long (in bytes) can the table’s data file (.ISD) get. Max keyfile length How long (in bytes) can the table’s key file (.ISM) get. Recordlength How much space does each record/row take. Record format Which format does each record/row have. This example uses Fixed length. table description A list of all keys in the table. For each key some low level information is presented. Key This key’s number. Start Where in the record/row does this index-part start. 67

Len How long is this index-part. For packed numbers this should always be the full length of the field. For strings it may be shorter than the full length. Index unique or multip.. If one value can exist multiple times in this index. Type What data-type does this index part have. This is a C data-type with the options packed, stripped or empty. Root Address of the root index block. Blocksize The size of each index block. This is by default 1024 but may be changed a compile time. Rec/key This is a statistical value used by the optimiser. It tells how many records there are per value for this key.

A unique key always has a value of 1. This may be updated after a table is loaded (or greatly changed) with isamchk -a. If this is not updated at all, a default value of 30 is given.

The 9th key is a multiple part key with two parts. isamchk -eis table_name Shows only the most important information from a table. Slow since it must read the whole table. Checking ISAM file: company.ISM Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 98% Packed: 17% Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Recordblocks: 1403698 Deleteblocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1626.51, System time 232.36 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 627, Swaps 0 Blocks in 0 out 0, Messages in 0 out 0, Signals 0 Voluntary contexts switches 639, Involuntary contexts switches 28966 Keyblocks used How many percent of the keyblocks are used.

Since this table has just been reorganised with isamchk the values are very high (very near theoretical maximum). Packed MySQL tries to pack keys with a common suffix. This can only be used for CHAR/VARCHAR/DECIMAL keys. For long strings like names, this can significantly reduce the space used. In the above example the 4 key is 10 characters long and gets a 60% reduction in space.

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Max levels How deep is the btree for this key. Large tables with long keys get high values. Records How many rows does the table have. M.recordlength Average recordlength. For fixed tables this is the recordlength. Packed MySQL strips spaces from the end of strings. How many percent did we save by doing this. Recordspace used How many percent of the datafile is used. Empty space How many percent of the datafile is unused. Blocks/Record How many blocks are there per record. This is always 1 for fixed format tables. This value should stay as close to 1.0 as possible.

If it gets to great you can reorganise the table with isamchk. See section How to repair tables. [p 55] .

Recordblocks How many blocks are used. For fixed format, this is the same as the number of records. Deleteblocks How many blocks are deleted. Recorddata How many bytes of actual user data there are in the datafile. Deleted data How many bytes of deleted data there are in the datafile. Lost space If a record is updated to a shorter length some space is lost. This is the sum of all such losses. Linkdata When the dynamic format is used, blocks are linked with pointers (length 4-7 bytes). This is the sum of all such pointers.

isamchk -eiv table_name Same as above but tells you what it is being done.

Checking ISAM file: company.ISM Data records: 1403698 Deleted blocks: 0 - check file-size - check delete-chain index 1: index 2: index 3: index 4: index 5: index 6: index 7: index 8: index 9: No recordlinks - check index reference - check data record references index: 1 Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 2 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 - check data record references index: 3 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 4 69

Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 - check data record references index: 5 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 6 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 7 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 8 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 9 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 9% Packed: 17% - check records and index references [LOTS OF ROW NUMBERS DELETED] Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Recordblocks: 1403698 Deleteblocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1639.63, System time 251.61 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 10580, Swaps 0 Blocks in 4 out 0, Messages in 0 out 0, Signals 0 Voluntary contexts switches 10604, Involuntary contexts switches 122798 Here is the data file sizes of the table used above.

-rw-rw-r-- 1 monty tcx 317235748 Jan 12 17:30 company.ISD -rw-rw-r-- 1 davida tcx 96482304 Jan 12 18:35 company.ISM The MySQL compressed read only table generator pack_isam is an extra that you get when ordering more that 10 licenses or extended support. Since pack_isam is distributed binary only, pack_isam is only available on some platforms. Of course, all future updates to pack_isam is included in the price. pack_isam may at some time be included as standard when we get some kind of turnover for MySQL. pack_isam works by compressing each column in the table separately. The information needed to decompress is read into memory when the table is opened.

This gives a much better performance when accessing individual records as one only has to uncompress exactly one record, not a much larger disk block like when using stacker on MSDOS.

MySQL uses memory mapping (mmap) on compressed tables and falls back to normal read/write file usage if mmap did not work. Usually, pack_isam packs the datafile 40-70%. There is currently two limitations with pack_isam: After packing, the table is read only. It can’t pack blobs, yet. 70

Fixing these limitations is on our TODO but with low priority. pack_isam options: > pack_isam --help pack_isam Ver 5.0 for SOLARIS 2.5 on SPARCstation Copyright (C) 1994-1997 TcX AB & Monty Program KB & Detron HB. This is not free software. You must have a license to use this program This software comes with ABSOLUTELY NO WARRANTY Pack a ISAM-database to take much smaller space Keys are not updated, one must run isamchk -rq on datafile afterwards Usage: pack_isam [OPTIONS] -b, --backup Make a backup of the table as table_name.OLD -f, --force Force packing of table even if it’s gets bigger or tempfile exists.

-j, --join=# Join all given tables into table. All tables MUST be identical. -p, --packlength=# Force storage size of recordlength (1,2 or 3) -s, --silent Be more silent. -t, --test Don’t pack table only test packing it -v, --verbose Write info about progress and packing result -w, --wait Wait and retry if table is in use -T, --tmp_dir=# Use temporary directory to store temporary table - - debug=... output debug log. Often this is ’d:t:o,filename‘ - - help display this help and exit -V, --version output version information and exit Typical run: (/my/monty/tmp) ls -l station.* -rw-rw-r-- 1 monty my 994128 Apr 17 19:00 station.ISD -rw-rw-r-- 1 monty my 53248 Apr 17 19:00 station.ISM -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm (/my/monty/tmp) isamchk -dvv station ISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-02-02 3:06:43 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafilepointer (bytes): 2 Keyfile pointer (bytes): 2 Max datafile length: 54657023 Max keyfile length: 33554431 Recordlength: 834 Record format: Fixed length table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 1024 1024 1 2 32 30 multip.

text 10240 1024 1 Field Start Length Type 1 1 1 2 2 4 3 6 4 4 10 1 5 11 20 6 31 1 71

7 32 30 8 62 35 9 97 35 10 132 35 11 167 4 12 171 16 13 187 35 14 222 4 15 226 16 16 242 20 17 262 20 18 282 20 19 302 30 20 332 4 21 336 4 22 340 1 23 341 8 24 349 8 25 357 8 26 365 2 27 367 2 28 369 4 29 373 4 30 377 1 31 378 2 32 380 8 33 388 4 34 392 4 35 396 4 36 400 4 37 404 1 38 405 4 39 409 4 40 413 4 41 417 4 42 421 4 43 425 4 44 429 20 45 449 30 46 479 1 47 480 1 48 481 79 49 560 79 50 639 79 51 718 79 52 797 8 53 805 1 54 806 1 55 807 20 56 827 4 57 831 4 Compressing station.ISD: (1192 records) - Calculating statistics normal: 20 empty-space: 16 empty-zero: 12 empty-fill: 11 pre-space: 0 end-space: 12 intervall-fields: 5 zero: 7 Original trees: 57 After join: 17 - Compressing file 87.14% (/my/monty/tmp) ls -l station.* 72

-rw-rw-r-- 1 monty my 127874 Apr 17 19:00 station.ISD -rw-rw-r-- 1 monty my 55296 Apr 17 19:04 station.ISM -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm (my/monty/tmp) isamchk -dvv station ISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-04-17 19:04:26 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 1 Max datafile length: 16777215 Max keyfile length: 131071 Recordlength: 834 Record format: Compressed table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 10240 1024 1 2 32 30 multip.

text 54272 1024 1 Field Start Length Type Huff tree Bits 1 1 1 constant 1 0 2 2 4 zerofill(1) 2 9 3 6 4 no zeros, zerofill(1) 2 9 4 10 1 3 9 5 11 20 table-lockup 4 0 6 31 1 3 9 7 32 30 no endspace, not_always 5 9 8 62 35 no endspace, not_always, no empty 6 9 9 97 35 no empty 7 9 10 132 35 no endspace, not_always, no empty 6 9 11 167 4 zerofill(1) 2 9 12 171 16 no endspace, not_always, no empty 5 9 13 187 35 no endspace, not_always, no empty 6 9 14 222 4 zerofill(1) 2 9 15 226 16 no endspace, not_always, no empty 5 9 16 242 20 no endspace, not_always 8 9 17 262 20 no endspace, no empty 8 9 18 282 20 no endspace, no empty 5 9 19 302 30 no endspace, no empty 6 9 20 332 4 allways zero 2 9 21 336 4 allways zero 2 9 22 340 1 3 9 23 341 8 table-lockup 9 0 24 349 8 table-lockup 10 0 25 357 8 allways zero 2 9 26 365 2 2 9 27 367 2 no zeros, zerofill(1) 2 9 28 369 4 no zeros, zerofill(1) 2 9 29 373 4 table-lockup 11 0 30 377 1 3 9 31 378 2 no zeros, zerofill(1) 2 9 32 380 8 no zeros 2 9 33 388 4 allways zero 2 9 34 392 4 table-lockup 12 0 35 396 4 no zeros, zerofill(1) 13 9 36 400 4 no zeros, zerofill(1) 2 9 37 404 1 2 9 38 405 4 no zeros 2 9 39 409 4 allways zero 2 9 73

40 413 4 no zeros 2 9 41 417 4 allways zero 2 9 42 421 4 no zeros 2 9 43 425 4 allways zero 2 9 44 429 20 no empty 3 9 45 449 30 no empty 3 9 46 479 1 14 4 47 480 1 14 4 48 481 79 no endspace, no empty 15 9 49 560 79 no empty 2 9 50 639 79 no empty 2 9 51 718 79 no endspace 16 9 52 797 8 no empty 2 9 53 805 1 17 1 54 806 1 3 9 55 807 20 no empty 3 9 56 827 4 no zeros, zerofill(2) 2 9 57 831 4 no zeros, zerofill(1) 2 9 Go to the first [p 5] , previous [p 57] , next [p 75] , last [p 87] section, table of contents [p 1] . 74

Go to the first [p 5] , previous [p 65] , next [p 76] , last [p 87] section, table of contents [p 1] .

Adding functions to MySQL Adding new functions to MySQL If you need it as sql function (like SOUNDEX()), its real easy: 1. Add one line in sql_lex.cc defining the function name in the sql_functions array. 2. Add two lines in sql_yacc.y. On defines the preprocessor symbol yacc can define (this should be added at the beginning of the file). Then define the function parameters and create an ’item’ with these parameters. Check, for example, all occurrences of SOUNDEX in sql_yacc.y 3. In item_func.h declare a class inheriting from Item_num_func or Item_str_func depending on whether your function returns a number or a string.

4. In ‘item_func.cc’ add: double *Item_func_newname::val() If you are defining a number function or String *Item_func_newname::Str(String *str) If you are defining a string function. 5. You should probably also define the following function: void Item_func_newname::fix_length_and_dec() This should at least calcutate max_length based on the given arguments. max_length is the maximal number of chars the function may return. If the function can’t return a NULL, one should set maybe_null = 0. About string functions: 1. For string functions the ’String *str’ argument provides a string buffer that may be used to hold the result.

2. A string function should return the string that holds the result. 3. All current string functions tries to avoid to alloc any memory unless absolutely necessary! Go to the first [p 5] , previous [p 65] , next [p 76] , last [p 87] section, table of contents [p 1] . 75

Go to the first [p 5] , previous [p 75] , next [p 78] , last [p 87] section, table of contents [p 1] . ODBC Which operating systems does MySQL ODBC support? MySQL ODBC is a 32 bit ODBC (2.50) level 0 for Windows95 and NT. We hope somebody will port it to Windows 3.x. How should I report problems with MySQL ODBC? We have only tested ODBC with Admndemo, some C programs, Msquery and Excel.

To give some light about any problem we would like to have the log file from the ODBC manager (the log you get when requesting logs from ODBCADMIN) and a MYODBC log.

To get a MYODBC log, please put this MYSQL_DEBUG=d:t:O,filename in your AUTOEXEC.BAT and restart. The log will be written to file ‘filename’. Programs known to work with MyODBC. Most programs should work with MyODBC, but these we tested ourselves or got a conformation from some user that is works: Program Comment Access Wants a primary key and a timestamp in each record to allow updates. Fails if comparing with single floats. Excel Works. odbcadmin Test program for ODBC. Delphi One must use DBE 3.2 or newer. C++Builder Tested with BDE 3.0. The only known problem is that when the table schema changes, query fields are not updated.

BDE however does not seem to recognise primary keys, only the index PRIMARY, though this has not been a problem. How do I fill in the various fields in the ODBC administrator program?

There are three possibilities for specifying the server name on windows95: 76

1. Use the IP. 2. Add a file lmhosts with the following info: ip hostname For example: 194.216.84.21 my 3. Configure the PC to use DNS. Example of how to fill in the ’ODBC setup’. Data Source Name: test Description: This is my test database Server: 194.216.84.21 User: monty Password: my Port: These are default values to be given when prompting for a Driver connect. You don’t have to give ’server’, ’user’ or ’password’ in this screen. If port is not given the default port (3333) is used.

When connection to a ODBC source you have the option to change the server, user, password and port.

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Go to the first [p 5] , previous [p 76] , next [p 81] , last [p 87] section, table of contents [p 1] . Problems Why do I get ’Access denied’? Have you installed the MySQL grant tables with the script ’mysql_install_db’? Test by executing ’mysql -u root test’. This should not give an error. You can also check if you have a file ’user.ISD’ in the mysql database directory (ordinary install_dir/var/mysql/user.ISD). Remember that you have to do ’mysqladmin reload’ each time you change the grant tables.

Otherwise the old tables are still used!

For testing, you should start the mysqld demon with the --without-grant-tables option. Now you can change the MySQL grant tables and use the script mysqlaccess to check if your grants works. mysqladmin reload tells the mysqld demon to start using the new grant tables. Even if you have access problems with perl, python, or ODBC, always test your privilege problems with mysql -u user database or mysql -uuser -ppassword database. If you get the error ’Access denied’ when trying to connect to the database with mysql -u user database then you have a problem with the ’user’ table. Check this by doing mysql -u root mysql and select * from user.

You should get an entry with ’hostname’ and ’user’ matching your computers hostname and your username. If the client and the server is running on the same host and you haven’t used the --host option to mysql and you are not using MIT threads, ’localhost’ is a synonym for your hostname. The ’Access denied’ error message will tell you who you are trying to log in as, from which host you are trying to log in from and if you was using a password or not. You should normally have one entry in the user table that exactly matches your host and user, exactly as given in the error message.

If mysql -u root test works but mysql -h your_hostname -u root test gives ’Access denied’ then you don’t have the right name for your host in the user table. For example if you have an entry with host ’tcx’ in the ’user’ table, but your DNS tells MySQL that your hostname is ’tcx.subnet.se’ then the entry will not work. Test by adding a record with the IP of your host in the ’user’ table. You can, natuarally, also add a host with a wildcard (for example ’tcx%’) in the ’user table’ (but using hostnames ending with % is pretty insecure). When using MIT threads, localhost is never used. All connections to the mysqld demon is done by TCP IP and you must have your real hostname in ’user’ even if you are running the client on the same host as the server.

If you get the error ’Access to database denied’ then you have a problem with the db table. If the used entry in the db table has an empty hostname, check also the corresponding entry in the ’host’ table. If mysql -u user database works on the server machine, but mysql -u host -u user database doesn’t work on another client machine, then you don’t have the client machine in the ’user’ or the ’db’ table. If you can’t get password to work, remember that passwords must be inserted with the PASSWORD function. See section A example of permission setup. [p 29] If mysql -u user test works but mysql -u user other_database doesn’t work, you don’t have the other_database in the ’db’ table.

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If you get ’Access to database denied’ when using the SELECT ... INTO OUTFILE or LOAD DATA SQL commands then you probably don’t have the file_priv privilege set for you in the user table. If everything else fails, start the mysqld demon with: --debug=d,general,query. This will print info about the host and user that tries to connect and also information about each command issued. See section How to debug MySQL [p 25] . If you have any other problems with the MySQL grant tables and feel you must post the problem to the list, always add a dump of the MySQL grant tables. You can dump the tables with the ’mysqldump mysql’ command.

Post your problem with the mysqlbug script. See section How does the privilege system work? [p 26] How to run MySQL as a normal user.

mysqld (the MySQL server) can run as any user. In order to change mysqld to run as user USER, you’d have to the following: Stop the server if its running Change the database directories so that USER has read and write privliges priviliges to them: shell> chown -R USER /your/path/to/mysql/var start the server as user USER If you are using mysql.server to start mysqld when the system is rebooted, you should change mysql.server to call ’su’ to user USER. You don’t have to do anything to safe_mysqld to run as not root. At this point, your mysqld process would be running fine and dandy as user ’USER’.

One thing hasn’t changed though - the access permissions. By default (right after running the permissions table install script), only user ’root’ has access permission to the database. Unless you have changed that, it’s still true. This shouldn’t stop you from accessing MySQL when you’re logged in under a user other than root, just specify -u root to the client program. Note that accessing MySQL as root, by supplying -u root in the command line, doesn’t have ANYTHING to do with MySQL running as root, as a user or as anyone else. The access permissions and userbase of MySQL are completely separate from the UNIX users.

The only connection to the UNIX users us if you don’t use the -u option to clients. In this case the client will try to login into MySQL with your UNIX login name. If your UNIX box itself isn’t secured, you should probably at least put a password on the root users in the MySQL access tables, since any johndoe user can run ’mysql -u root dbname’ and do whatever he likes. Problems with file permissions If you have problems with file permissions, for example when creating a table mysql gives: "ERROR: Can’t find file: ’path/with/filename.frm’ (Errcode: 13)", then you might have the wrong value for environment variable UMASK.

Default umask is 0664. Fix: UMASK=432 export UMASK ./bin/safe_mysqld 79

Problems using DATE fields. The format of DATE is ’YYYY-MM-DD’. Actually nothing else is allowed (ANSI SQL). One should use this format to update or in the WHERE clause, ie select * from table_1 where idate >= ’1997-05-05’; As a convenience, MySQL automatically converts the date to a number if used in a number context. It is also smart enough to allow a ’relaxed’ string form when updating and in a WHERE with a compare to a TIMSTAMP, DATE or a DATETIME field. This means that the following works: insert into table_1 (idate) values (19970505) ; insert into table_1 (idate) values (’19970505’) ; insert into table_1 (idate) values (’1997-05-05’); insert into table_1 (idate) values (’1997.05.05’); insert into table_1 (idate) values (’1997 05 05’); select idate from table_1 where idate >= ’1997-05-05’; select idate from table_1 where idate >= 19970505; select mod(idate,100)1 from table_1 where idate >= 19970505; select idate from table_1 where idate >= ’19970505’; The following will not work: select idate from table_1 where strcmp(idate,’19970505’)=0; Because ’19970505’ is compared as a string to ’1997-05-05’.

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Go to the first [p 5] , previous [p 78] , next [p 87] , last [p 87] section, table of contents [p 1] . MySQL client tools and API’s MySQL C API The C API is distributed with MySQL. It is included in the libmysqlclinet library.It allows C programs to access a database. int mysql_affected_rows(MYSQL *mysql) Retrieves the number of affected rows by the last UPDATE, DELETE or INSERT. void mysql_close(MYSQL *mysql) Closes a server connection. MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd) Establish a connection to a MySQL server.

int mysql_create_db(MYSQL *mysql, const char *db) Create a database.

void mysql_data_seek(MYSQL_RES *res, uint offset) Seeks to an arbitrary row in a query result set. int mysql_drop_db(MYSQL *mysql, const char *db) Drop a database. int mysql_eof(MYSQL_RES *) Determine if last row has been read. char *mysql_error(MYSQL *mysql) The error message from last MySQL function. MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *handle) Find out what type a table field is. unsigned int *mysql_fetch_lengths(MYSQL_RES *mysql) Returns the length of all columns in a query result set.

MYSQL_ROW mysql_fetch_row(MYSQL_RES *mysql) Fetch the ’next’ row in the query result. void mysql_field_seek(MYSQL_RES *result, int field) Put the column cursor on column number field. void mysql_free_result(MYSQL_RES *result) Free memory used to store a query result. char *mysql_get_client_info(void) Return version information for the current client library. char *mysql_get_host_info(MYSQL *mysql) Returns name of server host. int mysql_get_proto_info(MYSQL *mysql) Get protocol version used by connection. char *mysql_get_server_info(MYSQL *mysql) Returns the version number of the server. 81

int mysql_insert_id(MYSQL *mysql) Returns ID generated for AUTO_INCREMENT field.

MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild) Return maching database names. MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild) Return maching field names. MYSQL_RES *mysql_list_processes(MYSQL *mysql) Get a list of the current server threads. MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild) Return maching table names. int mysql_num_fields(MYSQL_RES *result) Return the number of columns in a result set.

int mysql_num_rows(MYSQL_RES *result) Returns the number of rows in result set. int mysql_query(MYSQL *mysql, const char *query) Executes a SQL query. int mysql_real_query(MYSQL *mysql, const char *query, uint length) Executes a SQL query with length information. int mysql_reload(MYSQL *mysql) Reload the user permissions table in the server. int mysql_select_db(MYSQL *mysql, const char *db) Connect to a database. int mysql_shutdown(MYSQL *mysql) Shut down the database server. char *mysql_stat(MYSQL *mysql) Return server status in a string. MYSQL_RES *mysql_store_result(MYSQL *mysql) Reads a result set to the client.

MYSQL_RES *mysql_use_result(MYSQL *mysql) Initiate a dynamic result set for each row. Why is it that after mysql_query() returns success, mysql_store_result() sometimes returns NULL? It means one of the following: 1. Malloc failure.

2. The data couldn’t be read (Error on connection). 3. The statement was a statement which never returns data (INSERT or UPDATE or DELETE). You can always check if the statement should have given a result by checking that mysql_num_columns(MYSQL *) isn’t 0. If this is 0 the last query was a statement that does not return values INSERT, DELETE.... You have got an error if mysql_error(MYSQL *) isn’t empty! 82

What results can I get from a query? mysql_affected_rows(MYSQL *) returns the number of affected rows in the last query when doing an INSERT, UPDATE or DELETE.

Except, if DELETE is used without a where clause then the table is truncated which is much faster!. In this case it returns records affected as zero. mysql_insert_id(MYSQL *) returns the given ID of the last query when inserting a row into a table with a AUTO_INCREMENT key. See section How can I get the unique ID for the last row? [p 83] Some queries, LOAD DATA INFILE... and INSERT INTO ... SELECT , return additional info. The result is returned in mysql_info(MYSQL *). mysql_info() returns a null pointer if there is no additional information.

How can I get the unique ID for the last row? If you insert a record that has a AUTO_INCREMENT key then you can get the given id with mysql_insert_id(MYSQL *). The last value is also stored in the server and can be retrieved with the LAST_INSERT_ID() function. You can check if an auto_increment key is used by the following code. This also checks if the query was a insert with a auto_increment key. if (mysql_error(MYSQL)[0] == 0 && mysql_num_fields(MYSQL_RESULT) == 0 && mysql_insert_id(MYSQL) != 0) used_id = mysql_insert_id(MYSQL); When using mysql_perl you can do something like: $std=$dbh->query("insert into foo (auto,text) values(NULL,’text’)"); print $std->insert_id; With DBD-mysql you can do something like: $dbh->do("INSERT INTO foo (auto,text) VALUES(NULL,’text’)"); print $dbh->func("_InsertID"); With ODBC you can do something like this: INSERT INTO foo (auto,text) VALUES(NULL,’text’) select LAST_INSERT_ID() or even INSERT INTO foo (auto,text) VALUES(NULL,’text’) INSERT INTO foo2 (id,text) VALUES(LAST_INSERT_ID(),’text’) What is the difference between mysql_use_result() and mysql_store_result() modes?

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mysql_use_results reads the result directly from the server without storing it in a local differ. This is somewhat faster and uses much less memory. One shouldn’t use mysql_use_results if there is a lot of processing being done for each row at the client side, or if the output is sent to a screen on which the user may do a ^S (stop scroll). Doing this would tie up the server and then other threads can’t update the used tables. One can’t use mysql_data_seek when using mysql_use_result.

Problems linking with C API. When linking with the C API you can get the following errors on some systems: gcc -g -o client test.o -L/usr/local/lib/mysql -lmysqlclient -lsocket -lnsl Undefined first referenced symbol in file floor /usr/local/lib/mysql/libmysqlclient.a(password.o) ld: fatal: Symbol referencing errors.

No output written to client This means that on your system you have to include the math library (-lm) last in the compile/link line. How to make a threadsafe client The client is ’almost’ thread-safe. The biggest problem is that net.c (the subroutines that read from sockets) are not interrupt safe. This was done with the thought that one may want to have one’s own alarm that can break a long read to a server.

The standard client libraries are not compiled with the thread options. To get a thread safe client use the -lmysys, -lstring and -ldbug libraries and net_serv.o that the server uses. When using a threaded client I think one can have great use of the thr_alarm.c routine. If you are using the mysys routines, the only thing one has to remember is to call my_init() first! Making a threadsafe client All functions except mysql_connect() are currently thread safe. To get connect thread_safe you have to do the following: Recompile the client with: CPPFLAGS=-DTHREAD_SAFE_CLIENT ./configure .... You may get some errors because of undefined symbols when linking the standard client as the pthread libraries are not included by default.

The resulting libmysqld.a library is now thread safe. Two treads can’t use the same handle (returned by mysql_connect()) at the same time, even if two threads can use different MYSQL_RES handles that was created with mysql_store_result(). 84

When using a threaded client one can have great use of the thr_alarm.c routine. If you are using the mysys routines, the only thing one has to remember is to call my_init() first! What is the difference between different thread packages? There are at least three types of thread packages. User threads in a single process; Thread switching is managed with alarms and the threads library manages all not thread- safe functions with locks.

Read, write and select are usually managed with a thread-specific select that switches to another thread if the running threads have to wait for data. If the user thread packages are integrated in the standard libs (FreeBSD and BSDI threads) the thread package requires less overhead than thread packages that have to map all unsafe calls (MIT-threads, FSU-threads and RTS threads). In some environments (for example SCO), all system calls are thread- safe so the mapping can be done very easily (FSU-threads on SCO). Downside: All mapped calls take a little time and it’s quite tricky to be able to handle all situations.

There are usually also some system calls that are not handled by the thread package (like MIT-threads and sockets). Thread scheduling isn’t always optimal. User threads in separate processes; Thread switching is done by the kernel and all data is shared between threads. The thread package manages the standard thread calls to allow sharing data between threads. Linuxthreads is using this method. Downside: Lots of processes. Thread creating is slow. If one thread dies the rest are usually left hanging and one has to kill them all before restarting. Thread switching is somewhat expensive.

Kernel threads; Thread switching is handled by the thread library or the kernel and is very fast. Everything is done in one process but ’ps’ may on some systems show the different threads. If one thread aborts the whole process aborts. Most system calls are threadsafe and should require very little overhead. Solaris, HPUX, AIX and OSF1 has kernel threads. In some systems kernel threads are managed by integrating user level threads in the system libraries. In such cases, the thread switching can only be done by the thread library and the kernel isn’t really ’thread aware’.

MySQL Perl API’s mysqlperl DBD::mysql MySQL JAVA connectivity (JDBC) MySQL C++ API’s MySQL TCL API’s 85

MySQL Python API’s MySQL Python API’s Go to the first [p 5] , previous [p 78] , next [p 87] , last [p 87] section, table of contents [p 1] . 86

Go to the first [p 5] , previous [p 81] , next, last section, table of contents [p 1] . How does MySQL compare with other databases How does MySQL compare with mSQL This section has been written by the MySQL developers so it should be read with that in mind. But there are NO factual error that we know of. Performance. For a true comparison of speed so the growing MySQL benchmarks suite. It is meant to be a benchmark that will tell any user which SQL is good at what.

Because of no thread creation overhead, small parser, few features and simple security mSQL should be quicker at: Test that do a lot of connect/disconnect with a very simple query. Inserts into very simple tables with few fields and keys. CREATE TABLE and DROP TABLE.

SELECT one something that isn’t a key. (A table scan is very easy) As these operations are so simple, it is hard to be better at them when you have a higher start overhead. After the connection is established MySQL should perform much better. MySQL on the other hand is much faster than mSQL and most other SQL implementions on the following: Retrieving large results (MySQL has a better, faster and safer protocol) Tables with variable length strings since MySQL has more efficent handling and can have keys on varchars.

Handling tables with many fields (columns). Handling tables with large record lengths.

SELECT with many expressions. SELECT on large tables. Handle many connections at the same time. MySQL handles with multiple threads. mSQL will take care of one connection at a time. This problem only exists on MySQL if you make long update statements (like updating the whole table) and even in those cases other threads can continue to work with other tables. Joins (I have seen speed differences of 50 times on this one). ORDER BY and GROUP BY.

DISTINCT. Using TEXT or BLOB columns. Disk space efficiency That is, how small can you make your tables. MySQL has very precise types so that use can create tables that take very little space. An example of a useful MySQL datatype is the mediumint that is 3 bytes long. If you have 10.000.0000 records even saving one byte per record is very important. Since mSQL2 only has 4 types (char,text,int,real) it is hard to get small tables. Stability This is harder to judge objectively. For MySQL stability see See section How stable is MySQL? [p 52] . We have no experience with mSQL stability so we can not say anything about that.

Price Another important issue is of course the license. MySQL has a more flexible license than mSQL and is also cheaper than mSQL. Remember to at least consider paying for a license or email support for whatever product you choose to use. If you sell a product with MySQL you are of 87

course required to get a license for this. Perl interfaces MySQL has basically the same interfaces to perl as mSQL with some added features. JDBC (Java) MySQL has a java interface by GWE technologies that has been improved by Xiaokun Kelvin ZHU. We know that mSQL has one but we have too little experience with it to compare. Rate of development MySQL has a very small team of developers, but we are quite use to coding C and C++ very rapidly. Since threads, functions, group by and so on are still not implemented in mSQL, it has a lot of catching up to do. To get some perspective on this you can view the mSQL HISTORY file for the last year and compare it with MySQL NEWS file.

It should be pretty obvious which one has developed most rapidly.

Utility programs Both mSQL and MySQL has a lot of interesting third party tools. Since it is very easy to port upwars (mSQL -> MySQL) MySQL has almost all interesting mSQL applications. MySQL comes with a simple msql2mysql program that fixes the different spelling of the most used functions. A conversion of a client program from mSQL to mySQL usually takes a couple of minutes. How about mSQL tools like msql-tcl, msqljava? According to our experience it would just take a few hours to convert a tool using the mSQL C API to the MySQL C API.

The procedure: 1. Run the shell script msql2mysql on the source.

This needs the binary program replace, which is distributed with MySQL. 2. Compile 3. Fix all compiler errors: Differences between the MySQL and mSQL C API’s. MySQL uses MySQL as a connection type (mSQL uses an int). MySQL connect takes a pointer to a MYSQL structure as a parameter. It is easy to define one globally or use malloc to get one. mysql_connect takes 2 extra parameters. You may set these to NULL,NULL for default use (user and password).

mysql_error takes the MYSQL structure as a parameter. Just add the parameter to your old msql_error code if you are porting old code. Some incompatibilities exist as a result of MySQL supporting multiple connections to the server from the same process. MySQL returns a error number and a text for all errors. mSQL only returns a text error How different from mSQL are the MySQL client/server communications protocols? 88

There are enough differences that it is impossible (at least not easy) to support both. The greatest differences between MySQL and mSQL are: A message buffer may contain many result rows.

The message buffers are dynamically enlarged if the question or the result is bigger than the current buffer up to a configurable server and client limit. All packages are numbered to catch out dupplicated or missing packets. All columns are sent in ASCII, the length of columns and rows are sent in packed binary coding (1,2 or 3 bytes).

MySQL can read in the result unbuffered (without having to store the full set in the client). If a single write/read takes more than 30 seconds then the server closes the connection. If nothing has happened on a connection for 8 hours the server closes the connection. We don’t think it makes sense to give a full specification of the connection protocol as we have plans to optimize this in the near future. What are the differences in the SQL syntax between MySQL & mSQL 2.0? CREATE TABLE MySQL Has the following column option types: See section CREATE TABLE syntax. [p 36] UNSIGNED for integer columns.

ZEROFILL for integer columns. AUTO_INCREMENT for integer columns. See section How can I get the unique ID for the last row? [p 83] DEFAULT values for all columns. MySQL also have many more types than ANSI SQL. mSQL To create indexes. MySQL All indexes have to be given to CREATE TABLE. Indexes can not be removed without recreating the table. See section ALTER TABLE syntax [p 37] . mSQL Indexes must be created by a separate CREATE INDEX clause. Indexes may be removed with DROP INDEX. To get a unique identifier in a table at insert. MySQL Use autoincrement as a column type specifier. See section How can I get the unique ID for the last row? [p 83] mSQL Create a SEQUENCE on a table and use the __seq function to get a unique index.

Group functions (functions that can be used in a SQL group by clause). MySQL count(), avg(), min(), max(), sum() and std(). min() and max() may take string arguments. count(*) is optimised to return very quickly if this is the only thing in the query: 89

SELECT COUNT(*) FROM table_name mSQL Does not support GROUP BY yet. How do I search independent of character case? MySQL LIKE is always case independent. If possible MySQL uses indexes if the like argument doesn’t start with a wild-card. mSQL Use CLIKE. How do I search with regular expressions? MySQL Use REGEXP or RLIKE. The syntax should be basically POSIX. mSQL Use RLIKE. What are the differences in the WHERE statement? MySQL MySQL does everything according to mathematical priorities (AND is evaluated before OR). To get mSQL behaviour in MySQL, use brackets: select * from table where a=1 and b=2 or a=3 and b=4 -> select * from table where (a=1 and (b=2 or (a=3 and (b=4)))).

mSQL Evaluates everything from left to right. That means that some logical calculation with more that 3 arguments can not be expressed. Qualifying column names MySQL If a column name is unique you do not have to use the full qualifier. mSQL When using more than one table in a select you must use full table qualifiers. Aliasing MySQL Has table and column aliasing. mSQL Has table aliasing. Insert/update with calculations. MySQL Full calculation support. In a insert you may use values of preceding columns. mSQL Only insert update with constants. Which formulas may be used in the select statement MySQL Too many to print here.

See section SELECT syntax [p 39] . mSQL No functions are supported yet. SQL HAVING clause.

MySQL Supported, but can only use calculation on the selected columns. To select on a calculated value one must use a column alias. Ex: SELECT COUNT(*) AS id_count,id FROM groups GROUP BY id HAVING id_count > 10. 90

mSQL Not supported. Access Control MySQL Has tables to store grant options per user, host and db. See section How does the privilege system work? [p 26] mSQL Has a file ‘mSQL.acl’ where you can grant read/write privileges for users. Threads MySQL Is multi-threaded. Each connection has it is own thread, which means that none of them has to wait for the other (unless a data-modifying query is executed).

mSQL All other connections have to wait until the first, doesn’t matter whether the query is long or short, is executed and finished. After that the next connection can be served, while the others wait again, etc.

Speed MySQL is significantly quicker on complex selects than mSQL. Problems with AND and OR priority Remember that AND has higher priority in boolean algebra than OR. It is like 1+2*3 is = 1+ (2*3) = 7. Always when you are in doubt: 1. Remove all distinct keywords to make the query easier to debug. 2. Write all fields from all tables to really see what you are doing. This will make it easier to see what goes wrong. Distinct may also be a lot slower than a normal select. Go to the first [p 5] , previous [p 81] , next, last section, table of contents [p 1] . 91