User Management

I have an install with several thousand users. I have many that I would like to delete based on certain characteristics of their user name. For example, delete any user account with a username "*xyz"

Is there a problem with deleting users via sql query rather than using drupal admin to do this? It would be a great time savings to do it via query, but I don't know if just deleting from the user table is enough/would cause any problems.

Any ideas are greatly appreciated. Thanks!

TonyV