[Mediawiki-l] How to determine if string exists within any username in database

What php code is needed to determine if "394433" exists at the end of any username?

myphpadmin created the following sql: SELECT * FROM `user`WHERE `user_name` LIKE CONVERT( _utf8 '%395523%'USING latin1 )

but I can't find any meta article explaining how to make such a query and return a boolean value:

This would be used to trigger a rename_user function.

Overview- Our Single Sign-on process provides a unique username in the form of firstname_lastname_ID (the ID never changes but the name could due to marriage). If this username exists within MediaWiki, the user is logged-in. If not, an extension creates a new user. I need the above check(and rename_user function) prior to creating a new user.

This is a tangent discussion to "Best strategy to populate User data from Single Sign On?" http://mail.wikipedia.org/pipermail/mediawiki-l/2006-April/011719.html but may apply to a wider audience....

Thanks in advance for any response.. bc