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From Jacques Nadeau <jacq...@apache.org>
Subject Re: Collation meets relational algebra
Date Sun, 02 Aug 2015 03:23:31 GMT
:D

On Sat, Aug 1, 2015 at 7:02 PM, Julian Hyde <jhyde.apache@gmail.com> wrote:

> 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 <jacques@apache.org> 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 <jhyde@apache.org> 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
> >>
> >>
>
>

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