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!