maria-developers team mailing list archive

[Roberto Spadim <roberto@xxxxxxxxxxxxx>]

Hi Reindl Harald
Maybe we have a problem... i think it's not part of 4978, but maybe it's a
documentation problem? well i don't know, but please check this comment
from Sergei at MDEV-5007


Sergei Golubchik<https://mariadb.atlassian.net/secure/ViewProfile.jspa?name=serg>
added
a comment - 14 minutes ago
The explanation is in the knowledge base
https://mariadb.com/kb/en/why-is-order-by-in-a-from-subquery-ignored/

But here it is, again: your ORDER BY clause is ignored by the optimizer. It
is not a bug.

A "table" (and subquery in the FROM clause too) is — according to the SQL
standard — an unordered set of rows. Rows in a table (or in a subquery in
the FROM clause) do not come in any specific order. That's why the
optimizer can ignore the ORDER BY clause that you have specified. In fact,
SQL standard does not even allow the ORDER BY clause to appear in this
subquery (we allow it, because ORDER BY ... LIMIT ... changes the result,
the set of rows, not only their order).

You need to treat the subquery in the FROM clause, as a set of rows in some
unspecified and undefined order, and put the ORDER BY on the top-level
SELECT.


2013/9/10 Reindl Harald <h.reindl@xxxxxxxxxxxxx>

>
>
> Am 10.09.2013 16:55, schrieb Roberto Spadim:
> > Hi guys!
> > I posted the MDEV-5007 and it's a old problem from MDEV-3795 (the same
> problem)
> > It (MDEV-3795) was closed as a not a bug, but i think it's a bug, but i
> didn't explained well at the first time
> >
> > I changed from a mysql server to a mariadb server and the result order
> by isn't executed, i tried
> > myisam,aria,innodb,memory engines and all of them return the same
> problem (order by not executed)
> >
> > On the wrong query i don't see the "using filesort" at explain, and at
> the right query (with right order by) it
> > show "using filesort"
> >
> > Could anyone help me? or at least EXPLAIN why the order by shouldn't be
> executed on the first query, and maybe a
> > workaround using sql_optimizer variable or something like it?
> >
> > it's a closed software and i need to contact developer to change the
> query, that's why i'm talking about the
> > sql_optimizer variable instead of rewrite the query
>
> this is pretty clear the following and will be fixed in 5.5.33
> https://mariadb.atlassian.net/browse/MDEV-4978
>
>


-- 
Roberto Spadim
SPAEmpresarial