Careful with making the database adhere to people’s “expectations". MySQL used to guarantee that the output of GROUP BY is sorted and they lived to regret it.
> On Aug 1, 2015, at 8:58 AM, Jacques Nadeau <[email protected]> wrote: > > I think Aman and Vicki mentioned that this is a situation where most > databases diverge from the spec since people have a certain expectation. > > On Fri, Jul 31, 2015 at 9:56 PM, Julian Hyde <[email protected]> wrote: > >> >>> Jinfeng, the subquery's ORDER-BY can be dropped in some cases but not >> all.. >>> for instance in the following query: >>> SELECT a1 FROM (SELECT a1 FROM t1 WHERE .... ORDER BY a1) LIMIT 10; >>> The OB should not be dropped. There are other cases, this is one >> example. >> >> FWIW, My understanding of the SQL standard is that that ORDER BY can be >> dropped. You can’t rely on the order of output from a sub-query. If you >> want the desired effect you have to combine ORDER BY and LIMIT into the >> same clause. >> >> Julian >> >>
