title: Retrieve value from column depending on another column
body: <p>From this table of football players, how would you select the players' names alongside their captains' names?</p>
  
  <pre><code>PlayerID | PlayerName | TeamCaptainID
  =====================================
  1        | Jay        | 5
  2        | John       | 3
  3        | James      | 3
  4        | Jack       | 5
  5        | Jeremy     | 5
  </code></pre>
  
  <p>The result I'm after is:</p>
  
  <pre><code>Player | Captain
  ================
  Jay    | Jeremy
  John   | James
  James  | James
  Jack   | Jeremy
  Jeremy | Jeremy
  </code></pre>