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

The function pass_down_bound() is a recursive function. For
SubqueryScanState we have to do something similar to ResultState i.e.
call pass_down_bound() recursively on subqueryScanState->subplan.

Please add this to the next commitfest.

On Wed, Apr 19, 2017 at 6:09 AM, Douglas Doole <dougdoole@gmail.com> wrote:
> We've hit a case where pass_down_bound() isn't pushing the row count limit
> from limit into sort. The issue is that we're getting a subquery scan node
> between the limit and the sort. The subquery is only doing column projection
> and has no quals or SRFs so it should be safe to push the limit into the
> sort.
>
> The query that hit the problem can be simplified to:
>
>    SELECT * FROM (SELECT A,B FROM T ORDER BY C) LIMIT 5
>
> (Yeah, the query's a little screwy in that the ORDER BY should really be
> outside the subselect, but it came from a query generator, so that's a
> different conversation.)
>
> Proposed patch is attached.
>
> - Doug
> Salesforce
>
>
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-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company