title: Postgres append or set each elements(if not exists) of an array to an array column
body: <p>If I have</p>
  
  <pre><code>select arr_str from tabl1;
  -&gt; {'a', 'b'}
  </code></pre>
  
  <p>then how do I add this <code>{'b','c','d'}</code> array to column <code>arr_str</code>
  so that I would get the following result</p>
  
  <pre><code>select arr_str from tabl1;
  -&gt; {'a', 'b', 'c', 'd'}
  </code></pre>
  
  <p>I don't want to <strong>SELECT</strong> the column and create a new array for updating. I only want to use <strong>UPDATE</strong> query.</p>