title: Does "group by" automatically guarantee "order by"?
body: <p>Does "group by" clause automatically guarantee that the results will be ordered by that key? In other words, is it enough to write:</p>
  
  <pre><code>select * 
  from table
  group by a, b, c
  </code></pre>
  
  <p>or does one have to write</p>
  
  <pre><code>select * 
  from table
  group by a, b, c
  order by a, b, c
  </code></pre>
  
  <p>I know e.g. in MySQL I don't have to, but I would like to know if I can rely on it accross the SQL implementations. Is it guaranteed?</p>