title: DB2 insert if not present and select
body: <p>I have a DB2 database table </p>
  
  <pre><code>Users
  ------
  userId: BIGINT
  </code></pre>
  
  <p>I need to return a row from the table for a user. If the row is not present it should be inserted and returned. 
  Is there a single statement that can do this</p>