Subject: Re: Throwing unnecessary joins away
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: =?ISO-8859-1?Q?Ott=F3_Havasv=F6lgyi?= <havasvolgyi.otto@gmail.com>
Cc: pgsql-performance@postgresql.org
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Date: Thu, 12 Jan 2006 11:03:02 -0600

On Thu, 2006-01-12 at 11:00, Ott=C3=B3 Havasv=C3=B6lgyi wrote:
> Hi,
>=20
> I think it would be sufficient only for views. In other cases the
> programmer can optimize himself. But a view can be a join of other
> tables, and it is not sure that all of them are always needed. It all
> depends on what I select from the view.

The idea that you could throw away joins only works for outer joins.=20
I.e. if you did:

select a.x, a.y, a.z from a left join b (on a.id=3Db.aid)=20

then you could throw away the join to b.  But if it was a regular inner
join then you couldn't know whether or not you needed to join to b
without actually joining to b...