| From: | Moshe Jacobson <moshe(at)neadwerx(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Postgres-Bugs <pgsql-bugs(at)postgresql(dot)org>, Robert Mowlavi <robert(at)neadwerx(dot)com>, Chris Autry <chris(at)neadwerx(dot)com> |
| Subject: | Re: LEFT JOINs not optimized away when not needed |
| Date: | 2014-07-09 17:37:25 |
| Message-ID: | CAJ4CxLn7QHOHVYeHWntEn-J4FS_gCT-m39jNzokbdYAZbkVoOg@mail.gmail.com |
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| Lists: | pgsql-bugs pgsql-hackers |
On Wed, Jul 9, 2014 at 1:33 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Right. Yeah, I was not that excited about its usefulness either.
> However, the OP seems to think that it's a common optimization
> (I wonder if he can cite chapter and verse on which other DBMSes
> do it).
>
I make no claim about its commonness, but I think this type of optimization
is very useful when selecting a limited subset of the columns from a
complex view, particularly where the output rows are expected to be
distinct on the exact set of columns that are selected.
Moshe Jacobson
Manager of Systems Engineering, Nead Werx Inc. <http://www.neadwerx.com>
2323 Cumberland Parkway · Suite 201 · Atlanta, GA 30339
"Quality is not an act, it is a habit." -- Aristotle
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