title: Single query for "INSERT INTO table if column value not found"
body: <p>How can I use a single query for inserting table when a column value is not found.
  eg/ i want to insert new user only when this username not found</p>
  
  <p>what i doing now is issue 1 query to check for existing,
  then another query if no existing found. total 2 query</p>
  
  <pre><code> INSERT INTO friends (memberID) SELECT 1 WHERE NOT EXISTS (SELECT memberID FROM friends WHERE memberID =  1)
  </code></pre>