title: PostgreSQL SELECT last array key from text[] array column
body: <p>How do I <code>SELECT</code> only the last key from an array column?</p>
  
  <pre><code>SELECT * FROM table;
  
  +----+---------------+
  | id | col_array     |
  +----+---------------+
  | 1  | {"a"}         |
  +----+---------------+
  | 2  | {"a","b","c"} |
  +----+---------------+
  | 3  | {"b","d","f"} |
  +----+---------------+
  </code></pre>
  
  <p>The desired result for <code>col_array</code> would be: a, c, f.</p>