[Yashas]

Before you ban try this(Simple Way):

Quote:

SELECT Username FROM 'your_table' WHERE Username='PLAYERNAME'

Then use mysql_num_rows to get if any row exists.
If it returns 0 then the user doesn't exist.

Or check after you send the BAN query.If it returns a value then the player has been banned or else nothing happens to the database and you'll come to know that user doesn't exist.This method eliminates an additional query.