title: Why doesn't "COALESCE" work with "GROUP BY"?
body: <p>I have a table <code>table</code> with this data:</p>
  <pre><code>+----------+------+----------+
  | location | sold | scrapped |
  +----------+------+----------+
  | Paris    | 5    | NULL     |
  | Paris    | NULL | 6        |
  +----------+------+----------+
  </code></pre>
  <p>I want this:</p>
  <pre><code>+----------+------+----------+
  | location | sold | scrapped |
  +----------+------+----------+
  | Paris    | 5    | 6        |
  +----------+------+----------+
  </code></pre>
  <p>Why doesn't this query do that?</p>
  <pre><code>SELECT `location`,
         coalesce(`sold`)     AS `sold`,
         coalesce(`scrapped`) AS `scrapped`
  FROM `table`
  GROUP BY `location`
  </code></pre>