From: Tom Lane <tgl@sss.pgh.pa.us>
To: Moises Lopez <moylop260@vauxoo.com>
cc: pgsql-performance@lists.postgresql.org
Subject: Re: The query plan get all columns but I'm using only one column.
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Comments: In-reply-to Moises Lopez <moylop260@vauxoo.com>
	message dated "Fri, 24 Apr 2020 16:11:12 -0500"
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Date: Sat, 25 Apr 2020 10:24:23 -0400
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Moises Lopez <moylop260@vauxoo.com> writes:
>     ->  Seq Scan on public.link l1  (cost=0.00..10.40 rows=40 width=516)
> (actual time=0.010..0.011 rows=1 loops=1)
> *            Output: l1.id <http://l1.id>, l1.url, l1.name
> <http://l1.name>, l1.description, l1.rel*

This is normal; it is not a bug, and it is not a source of performance
issues either.  The planner is choosing to do that to avoid a projection
step in this plan node, because there's no need for one.  On the other
scan, where it *is* important to project out just the required columns to
minimize the size of the hash table above the scan, it does do so:

>             ->  Seq Scan on public.link l2  (cost=0.00..10.40 rows=40
> width=516) (actual time=0.010..0.011 rows=1 loops=1)
>                 Output: l2.url

> Is there a manner to avoid returning all columns in order to get a better
> performance?

You have not shown us anything about what your actual performance
issue is, but this isn't it.

https://wiki.postgresql.org/wiki/Slow_Query_Questions

			regards, tom lane