title: CASCADE DELETE on two foreign key constraints
body: <p>I have the following example:</p>
  
  <pre><code>Table A
     -some_id
  
  Table B
     -another_id
  
  Table C
     -some_id_fk
     -another_id_fk
  </code></pre>
  
  <p>I want to cascade a row on <code>Table C</code> if both <code>some_id</code> and <code>another_id</code> are deleted from their respective tables. </p>
  
  <p>How can I make a row in Table C cascade itself when two foreign keys are deleted? </p>
  
  <p>If only one of the FKs is deleted, the affected row should change to a null value in the column referencing that foreign key.</p>