Re: Why does the number of rows are different in actual and estimated.

From: Claudio Freire <klaussfreire(at)gmail(dot)com>
To: AI Rumman <rummandba(at)gmail(dot)com>
Cc: Evgeny Shishkin <itparanoia(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, postgres performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Why does the number of rows are different in actual and estimated.
Date: 2012-12-14 19:12:56
Message-ID: CAGTBQpZfLp5C=qCR68UVOOrUXeSCoz_mJrkvM3+Svpahh+J4tg@mail.gmail.com
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On Fri, Dec 14, 2012 at 4:01 PM, AI Rumman <rummandba(at)gmail(dot)com> wrote:
> Does FK Constraint help to improve performance? Or it is only for
> maintaining data integrity?

I'm not entirely sure it's taken into account, I think it is, but a FK
would tell the planner that every non-null value will produce a row.
It seems to think there are a large portion of non-null values that
don't.

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