title: SQL SELECT from based on truth table
body: <p>How can I select the columns to be returned by a lookup truth table?
  my data:</p>
  <pre><code>| nam | X | Y |
  | Bob | 2 | 5 |
  | Jan | 1 | 6 |
  </code></pre>
  <p>the lookup table</p>
  <pre><code>| prop| SHOW |
  | nam | true |
  |  X  | false|
  |  Y  | true |
  </code></pre>
  <p>someting like <code>SELECT from data (columns which have &quot;true&quot; in lookup)</code> resulting in:</p>
  <pre><code>| nam | Y |
  | Bob | 5 |
  | Jan | 6 |
  </code></pre>