title: mysql multiple group_concat order preservation
body: <p>let's say I have a table <strong>mytable</strong>:</p>
  
  <p><code>select * from mytable</code>:</p>
  
  <p><code>
  +------+------+------+
  | a    | b    | c    |
  +------+------+------+
  |    1 |    1 | a    |
  |    1 |    2 | b    |
  +------+------+------+
  </code>
  I want to group both the columns <strong>b</strong> and <strong>c</strong> with <code>group_concat</code> function:</p>
  
  <p><code>select a, group_concat(b), group_concat(c) from mytable group by a</code></p>
  
  <p><code>
  +------+-----------------+-----------------+
  | a    | group_concat(b) | group_concat(c) |
  +------+-----------------+-----------------+
  |    1 | 1,2             | a,b             |
  +------+-----------------+-----------------+
  </code>
  My question is, do the mysql guarantee, that the <code>group_concat</code> will be always in the same order, that I won't get results like <strong>1, 2</strong> in the second column and <strong>b, a</strong> in the third column?</p>