title: How to exclude rows that don't join with another table?
body: <p>I have two tables, one has primary key other has it as a foreign key.</p>
  
  <p>I want to pull data from the primary table, only if the secondary table <strong>does not</strong> have an entry containing it's key. Sort of an opposite of a simple inner join, which returns only rows that join together by that key.</p>