Ok this is going to seem like a dumb question to experienced developers, but questions like this bother me until I ask them. So... is it more efficient to always run a delete query by default whether an entry exists or not, for example to delete a user name after a certain period of time (DELETE * from table where username=user), or should you check if that entry exists first using a select query and mysql_num_rows. What uses more processor on the server side? Obviously one approach contains more code, but I was wondering if certain mysql operations used a lot more cpu than others.