From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Ottó Havasvölgyi <havasvolgyi.otto@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Throwing unnecessary joins away
Date: Thu, 12 Jan 2006 11:03:02 -0600
Message-ID: <1137085382.3959.16.camel@state.g2switchworks.com> (raw)
In-Reply-To: <34608c0c0601120900l7d26073dp@mail.gmail.com>
References: <34608c0c0601120418n1af567b9n@mail.gmail.com>
<43C64CFB.9030504@barettadeit.com>
<34608c0c0601120541wd910da3s@mail.gmail.com>
<5269.1137081233@sss.pgh.pa.us>
<34608c0c0601120900l7d26073dp@mail.gmail.com>
On Thu, 2006-01-12 at 11:00, Ottó Havasvölgyi wrote:
> Hi,
>
> 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.
I.e. if you did:
select a.x, a.y, a.z from a left join b (on a.id=b.aid)
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...
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To: pgsql-performance@postgresql.org
Cc: smarlowe@g2switchworks.com, havasvolgyi.otto@gmail.com
Subject: Re: Throwing unnecessary joins away
In-Reply-To: <1137085382.3959.16.camel@state.g2switchworks.com>
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