Finding part of a text in a text field

[lunas]

Is it possible with mysql and or php to find part of text field? I've got my code writing usernames to a field using the concat function and now I need to check that field for a certain username and if it exists in that text field, then it is not to write it again.

Is there a function or way of searching the text field for the username?

Thanks.

[laserlight]

An example SQL query:
SELECT columns FROM table WHERE field LIKE '%search%'

[Sxooter]

Note that both MySQL and PostgreSQL have some type of regular expression matching built in as well. Postgresql can even supports regex matching in it's substring() functions...