Regular Expressions with Mysql

I must admit, this is something that I’ve never done until just recently; creating a regular expression in Mysql.  I’ve typically been able to accomplish whatever I wanted to with a LIKE statement or some server-side code.

However, just recently I updated the plugin I use to output sample code.  I was previously using a syntax of [codesyntax lang=”php”] and now I needed to change it simply be [code].  This wasn’t that simple since I’ve done hundreds of blogs with several different languages.  In searching I had over 15 distinct differences – hence, regular expressions to the rescue!

By default, Mysql has a built-in regular expression operator.  Documentation is here: http://dev.mysql.com/doc/refman/5.1/en/regexp.html. This works nicely for your standard regular expressions, but it’s a bit lacking in functionality.  A quick Google search brought me here: https://launchpad.net/mysql-udf-regexp.  Now this is quite nice, it implements three different regular expression operations as UDFs (User Defined Functions): REGEXP_LIKE, REGEXP_SUBSTR, REGEXP_INSTR, and a fourth for actual replacement of data: REGEXP_REPLACE.

The neat part of these functions is they include an optional third and fourth parameter for the position and occurrence of the regular expression match.  A nice addition when you only want to match to a specific occurrence of the string.

A nice simple regular expression as follows works nicely to grab them all:

[code]
(\[codesyntax)(.*?)(\])
[/code]

Now I can nice and quickly use the REGEXP_REPLACE function to change them all to [code].

If you are familiar with regular expressions in Oracle, these UDFs are meant to mimic them as closely as possible.