Re: [PATCH] Push limit to sort through a subquery

On Thu, Aug 17, 2017 at 11:36 AM, Douglas Doole <dougdoole(at)gmail(dot)com> wrote:

> I completely agree. The further a limit can be pushed down, the better.
>
> The patch looks good to me.
>

It seems like a somewhat ad-hoc approach; it supposes that we can take any
query produced by deparseSelectStmtForRel() and stick a LIMIT clause onto
the very end and all will be well. Maybe that's not a problematic
assumption, not sure. The grammar happens to allow both FOR UPDATE LIMIT n
and LIMIT n FOR UPDATE even though only the latter syntax is documented.

Regarding the other patch on this thread, you mentioned upthread that "If
it is possible to get more than one SubqueryScanState and/or ResultState
between the limit and sort, then the first block of code could be placed in
a while loop." I think that's not possible for a ResultState, but I think
it *is* possible for a SubqueryScanState.

--
Robert Haas
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