title: group by clause column name without selecting it in select list
body: <pre><code>select person
  from person
  inner join collectionmember
      on sourceobjectid=personid
  group by sourceobjectid 
  having count(sourceobjectid)&gt;1;
  </code></pre>
  
  <p>It is said that if we use group by clause the group by column name must be there in select column list,but above query works without selecting sourceobjectid.How this query works?</p>