Having is kind of like where, but only works with group by. It allows you to pick up groups that meets the criterias defined in having.

But having does not give you order, nor does group by. Although most of the DBMS systems actually do sorting for group by, it is not required by SQL standard, so unless it is clearly stated in document, don't assume it does the ordering.

For example, oracle does not always sort group by, but sometime it sorts. You will see this, when you do explain. Oracle will tell you whether it is 'sorted group by' or just a 'group by'. But this is not controled by you, so in Oracle, you still have to order by after group by, to ensure the ordering is really there. This does not degrade the performance, as Oracle will skip the order by silently, if the group by is 'sorted'.

In reply to Re^2: Ranking position in a SQL index by pg
in thread Ranking position in a SQL index by Anonymous Monk

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