title: Express SQL IF ELSE in Slick
body: <p>For example, how do I express this SQL in Slick?</p>
  
  <p><a href="https://stackoverflow.com/q/25284986">select column as true / false if id is exists in another table</a></p>
  
  <pre><code>join(Services).on(_.mid === _.id).map {
      case (m, s) =&gt; (m.id, m.name, ???).mapTo[SomeClass]
  }
  </code></pre>