Horton

Re: Pull up aggregate subquery

Hitoshi Harada <umi.tanuki@gmail.com>

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From: Hitoshi Harada <umi.tanuki@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2011-05-25T14:35:53Z
Lists: pgsql-hackers

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  1. Make NestLoop plan nodes pass outer-relation variables into their inner

2011/5/25 Hitoshi Harada <umi.tanuki@gmail.com>:
> So I'm still
> thinking which of pulling up and parameterized scan is better.

After more investigation I came up with third idea, pushing down
RangeTblEntry to aggregate subquery. This sounds like a crazy idea,
but it seems to me like it is slightly easier than pulling up
agg-subquery. The main point is that when you want to pull up, you
must care if the final output would be correct with other join
relations than the aggregate-related one. In contrast, when pushing
down the target relation to agg-subquery it is simple to ensure the
result.

I'm looking around pull_up_subqueries() in subquery_planner() to add
the pushing down logic. It could be possible to do it around
make_one_rel() but I bet query structure changes are doable against
Query, not PlannerInfo.

I appreciate any comments.

Regards,

-- 
Hitoshi Harada