title: Elegant way to remove orphan rows?
body: <p>I have a table with a lot of history entries that contain customer IDs.</p>
  
  <p>There is a separate customer table. Occasionally some of the customer entries are removed.</p>
  
  <p>Is there an easy way, without looping through each history entry, to drop all rows in the history table where the customer ID no longer exists because the customer row was deleted?</p>