title: use an if...else statement as a return value in sql
body: <p>I'm trying to write his in sql:</p>
  
  <pre><code>SET `Field` = (
      If `Field` is empty then "b", 
      if `Field` is not empty, concat(`Field`,"_b"))
  </code></pre>
  
  <p>Meaning, if <code>Field</code> had value a it would change to a_b, if it was empty, it would change to b
  Is there an sql synthax that creates this if..else statement properly?</p>