I want to execute a CREATE USER
statement, but only when the user doesn\'t already exist.
What would be the best way of doing this?
If you're creating a user, you need to create a grant too. The grant implicitly creates a user if it doesn't exist (which is why you are encouraged to include the password when creating a grant, just in case they don't exist). see http://dev.mysql.com/doc/refman/5.1/en/grant.html
So an option is to just create the grant (with the password) and the user is implicitly created.
E.g:
GRANT ALL PRIVILEGES ON db_name.*
TO 'user'@'%' IDENTIFIED BY 'password'
WITH GRANT OPTION;