title: MySQL one-to-many join with Group By only returns one observation
body: <p>I have a comment table and a tag table. For each comment, there could be multiple tags, or none. I want to join the two so I can get a list of tags for each comment. </p>
  
  <p>CommentTable:</p>
  
  <pre><code>+---------+----------+---+
  |CommentID|   Title  | ..|
  +---------+----------+---+
  |   1     |   animals|   |
  |   2     |   plants |   |
  +---------+----------+---+
  </code></pre>
  
  <p>TagTable:</p>
  
  <pre><code>+---------+----------+---+
  |  TagID  |CommentID | ..|
  +---------+----------+---+
  |    5    |     1    |   |
  |    6    |     1    |   |
  |    7    |     3    |   |
  +---------+----------+---+
  </code></pre>
  
  <p>So, a query should return the tags, (5,6) for a commentID == 1 and empty array for CommentID == 2</p>
  
  <p>This is what I have - it only selects the last ID and not multiples:</p>
  
  <pre><code>SELECT c.CommentID, c.Title,  t.TagID  FROM Comment as c
          LEFT OUTER JOIN Tag as t ON c.CommentID = t.CommentID
          GROUP BY t.TagID
  </code></pre>