title: Insert values if records don't already exist in Postgres
body: <p>I'd like to get this working, but Postgres doesn't like having the <code>WHERE</code> clause in this type of insert.</p>
  
  <pre><code>  INSERT INTO keys(name, value) VALUES
      ('blah', 'true')
    WHERE NOT EXISTS (
      SELECT 1 FROM keys WHERE name='blah'
    );
  </code></pre>