title: update all rows where there is a fk constraint issue
body: <p>I'm migrating a table into a new database. There is a fk constraint problem because there was never a relationship set between the 2 tables (tbl_contacts.contact_ID and tbl_communications.contact_ID which is the fk). I can see all the rows with </p>
  
  <pre><code>SELECT * FROM Farm.tbl_communication as S
  LEFT JOIN Farm.tbl_contacts ON S.contact_ID = Farm.tbl_contacts.contact_ID
  WHERE Farm.tbl_contacts.contact_ID IS NULL
  </code></pre>
  
  <p>I was just trying to delete those rows and I tried this:</p>
  
  <pre><code>    DELETE FROM Farm.tbl_communication 
      WHERE Farm.tbl_communication.contact_ID (SELECT contact_ID
      FROM ( SELECT * FROM Farm.tbl_communication) as S
      LEFT JOIN Farm.tbl_contacts ON S.contact_ID = Farm.tbl_contacts.contact_ID
      WHERE Farm.tbl_contacts.contact_ID IS NULL)
  </code></pre>
  
  <p>Which did not work. I have now thought better of it and I'm going to create a catch-all contact so I'll update all the communications.contact_ID with the new catch-all id. The problem is I have no idea how to go about that. what would the syntax be?</p>