title: HAVING statement on a GROUP_CONCAT field returns no result while the condition exists
body: <p>I'm having an issue with a HAVING clause on a string that is created by a GROUP_CONCAT statement.</p>
  <p>Running the query:</p>
  <pre><code>SELECT row_id, GROUP_CONCAT(cell_id,'-',cell_type) AS flat_row FROM `cells`
  GROUP by row_id;
  </code></pre>
  <p>returns the following:</p>
  <pre><code>|--------|-------------------------------------------------|
  | row_id | flat_row                                        |
  |--------|-------------------------------------------------|
  |      1 | 1-Text,6-Text,45-Text,5-Number,37-Text,9-Number |
  </code></pre>
  <p>However, running</p>
  <pre><code>SELECT row_id, GROUP_CONCAT(cell_id,'-',cell_type) AS flat_row FROM `cells`
  GROUP by row_id
  HAVING flat_row = '1-Text,6-Text,45-Text,5-Number,37-Text,9-Number';
  </code></pre>
  <p>returns 0 records.</p>
  <p>I was expecting to see the same result, does anyone know why the result is empty?
  The goal here is to check whether the database contains rows that have the exact cell composition provided in the <code>HAVING</code> clause.</p>