title: MySQL GROUP_CONCAT with ORDER BY
body: <p>I have a <code>SELECT</code> with a <code>GROUP_CONCAT</code> column as follows:</p>
  <pre><code>SELECT
      m.*,
      GROUP_CONCAT(s.id ORDER BY s.id ASC SEPARATOR ', ') AS schedule_ids
  
  FROM months m
  
  LEFT JOIN schedule s
      ON (MONTH(s.start_date) = m.id) OR (MONTH(s.end_date) = m.id)
  
  GROUP BY m.id
  </code></pre>
  <p>This column currently returns a comma separated string of 2 IDs, eg: <code>1, 2</code> or <code>11, 12</code>.</p>
  <p>I want to add an <code>IF</code> condition to the <code>ORDER BY</code>, whereby in the specific instance where the IDs returned are <code>1, 12</code>, the ORDER BY should be <code>DESC</code>, i.e. it should return <code>12, 1</code>, otherwise keep it as <code>ASC</code>.</p>
  <p>How can I do this?</p>