title: Is it more efficient to always run a delete query, or to check if that information exists first
body: <p>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 (<code>DELETE * from table WHERE username='user'</code>), or should you first check if the rows to be deleted exist using a <code>SELECT</code> query and checking <code>mysql_num_rows</code>. </p>
  
  <p>What uses more processor resources on the server side? </p>
  
  <p>Obviously one approach contains more code, but I was wondering if certain mysql operations used a lot more CPU than others.</p>