title: How do I find records that are not joined?
body: <p>I have two tables that are joined together. </p>
  
  <p>A has many B</p>
  
  <p>Normally you would do: </p>
  
  <pre><code>select * from a,b where b.a_id = a.id
  </code></pre>
  
  <p>To get all of the records from a that has a record in b. </p>
  
  <p>How do I get just the records in a that does not have anything in b?</p>