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Use PCRE regular expressions directly in MySQL
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config
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test
.gitignore
AUTHORS
COPYING
ChangeLog
INSTALL
Makefile.am
Makefile.in
NEWS
README.md
aclocal.m4
config.h.in
configure
configure.ac
from_php.c
from_php.h
ghfcns.c
ghfcns.h
ghmysql.c
ghmysql.h
installdb.sql
lib_mysqludf_preg_capture.c
lib_mysqludf_preg_check.c
lib_mysqludf_preg_info.c
lib_mysqludf_preg_position.c
lib_mysqludf_preg_replace.c
lib_mysqludf_preg_rlike.c
preg.c
preg.h
uninstalldb.sql

README.md

lib_mysqludf_preg - PREG functions for mysql

lib_mysqludf_preg is a library of mysql UDFs (user-defined-functions) that provide access to the PCRE (perl compatible-regular-expressions) library for pattern matching. The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl 5. This syntax can often handle more complex expressions and capturing than standard regular expression implementations. For more information about PCRE, please see: http://www.pcre.org/.

lib_mysqludf_preg currently provides the following functions:

PREG_RLIKE( pattern , subject ) - test whether subject matches pattern, which is a perl compatible regular expression.

PREG_CAPTURE(pattern, subject [, capture-group] [, occurence] ) - capture a named or numeric parenthesized subexpression from a pcre pattern. Capture from a specific match of the regex or the first match is occurence not specified.

PREG_CHECK( pattern ) - test whether the given pattern is a valid perl compatible regular expression.

PREG_POSITION(pattern, subject [, capture-group] [, occurence] ) - get the position in subject of a named or numeric parenthesized subexpression from a pcre pattern. Capture from a specific match of the regex or the first match if occurence not specified.

PREG_REPLACE(pattern, replacement, subject [ ,limit ] ) - perform a regular expression search and replace using a PCRE pattern.

LIB_MYSQLUDF_PREG_INFO() - obtain information about the currently installed version of lib_mysqludf_preg.

Some examples:

  • SELECT PREG_CAPTURE( '/(new)\s+([a-zA-Z])(.)/i' , description, 2 ) FROM state WHERE description LIKE 'new%' ;

  • SELECT PREG_POSITION( '/(new)\s+([a-zA-Z])(.)/i' , description, 2 ) FROM state WHERE description LIKE 'new%' ;

  • SELECT * from products WHERE PREG_RLIKE( '/hemp/i' , products.title )

  • SELECT PREG_REPLACE( '/fox/i' , 'dog' , 'The brown fox' )

Please see test/lib_udfmysql_preg.test and test/lib_udfmysql_preg.result for more examples.

More Documentation

Please see doc/html/index.html for more detailed documentation of the SQL functions.

Installation

Please see the file INSTALL or (doc/INSTALL.windows) for the full installation instructions.

The short instructions are:

./configure; make install; make installdb ; make test

Getting libmysql_udf_preg

Download from: http://www.goodhumans.com/Misc/libmysql_udf_preg-LATEST.tar.gz

Reporting Bugs & Feedback

Please send information regarding bugs and any other feedback to: raw@goodhumans.com

Known Issues & Caveats

  • pcre_study should be used (but isn't) for constant patterns;
  • there is no localization or locale support
  • there is no multi-byte character set support
  • some program locations that should be set in autoconf are not
  • It would be nice if there were a persistend cache of compiled regexes
  • It would also be nice if there were a peresistent cache of regex matches. This would allow for a more efficient way of retrieving multiple matches than repeated called with different 'occurence' arguments.

When & When not to use these UDF's

These UDF's are useful in the following circumstances: - you already have pcre regex's that need to be applied in mysql - you need to use a more complex regex than is supported by RLIKE - you need to capture portions of a regex from mysql - you are looking for a slight performance improvement over RLIKE

For optimal performance, these (or any) UDF's should not be used: - as a replacement for a prefixed LIKE or RLIKE (ie. LIKE 'foo%') - as a replacement for MATCH .. AGAINST ... IN BOOLEAN MODE. - on large databases without other query constraints. Often the PCRE (or any function or UDF) can be used in conjunction with a fulltext index constraint in order to reduce the number of rows the need to be operated on.
(ie. SELECT PREG_CAPTURE ... WHERE MATCH AGAINST)

Motivations & Explanations

-The 'occurence' argument to PREG_CAPTURE and PREG_POSITION was originally thought not to be needed, since the {} notation in the regex itself could be used. For instance, /.{2}(.)/ could be used to get the 3rd character of a string. This was found not to work for a large 'occurence'. (ie. /.{65536}(.)/)

Copyright and copying:

Copyright (C) 2007-2009 Rich Waters raw@goodhumans.com.

This file and most contents of this package are licensed under the GNU LESSER GENERAL PUBLIC LICENSE. Please see the COPYING.lesser file in this directory for details.

Acknowledgements

The amazing PCRE was written by Philip Hazel, and I use some of his code from the php preg extension in from_php.c

The documentation for this project is generated using doxygen which is available at: http://www.stack.nl/~dimitri/doxygen/

I referenced the following projects while trying to put together this library:

http://udf-regexp.php-baustelle.de/trac/ - a UDF that implements Oracle-like REGEX functions - written by Hartmut Holzgraefe

http://www.xcdsql.org/MySQL/UDF/lib_mysqludf_xql/lib_mysqludf_xql.html - A UDF that enables creation of XML - written by Arthur Daniels

Much of the documentation was generated using Doxygen, at http://www.stack.nl/~dimitri/doxygen/ , which was written by Dimitri van Heesch.

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