title: Postgresql from Json Object to array
body: <p>How can I convert a Postgresql stored json of this form</p>
  
  <pre><code>{"Kategorie": [{"ID": "environment", "ID": "economy"}]}
  </code></pre>
  
  <p>to get ["environment", "economy"] only using Postgresqls json flavoured syntax. The array in the stored source has here two elements, but may contain more (or only one). And the resulting array should result in all value elements.</p>