From: Ottó Havasvölgyi <havasvolgyi.otto@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Throwing unnecessary joins away
Date: Thu, 12 Jan 2006 14:41:30 +0100
Message-ID: <34608c0c0601120541wd910da3s@mail.gmail.com> (raw)
In-Reply-To: <43C64CFB.9030504@barettadeit.com>
References: <34608c0c0601120418n1af567b9n@mail.gmail.com>
<43C64CFB.9030504@barettadeit.com>
Hi,
As far as I know SQL Server has some similar feature. It does not join
if not necessary, more exactly: if the result would be the same if it
joined the table.
Here is another example:
http://www.ianywhere.com/developer/product_manuals/sqlanywhere/0902/en/html/dbugen9/00000468.htm
This would be a fantastic feature.
Best Regards,
Otto
2006/1/12, Alessandro Baretta <a.baretta@barettadeit.com>:
> Ottó Havasvölgyi wrote:
> > Hi all,
> >
> > Is PostgreSQL able to throw unnecessary joins?
> > For example I have two tables, and I join then with their primary keys,
> > say type of bigint . In this case if I don't reference to one of the
> > tables anywhere except the join condition, then the join can be eliminated.
> > Or if I do a "table1 left join table2 (table1.referer=table2.id)" (N :
> > 1 relationship), and I don't reference table2 anywhere else, then it is
> > unnecessary.
>
> It cannot possibly remove "unnecessary joins", simply because the join
> influences whether a tuple in the referenced table gets selected and how many times.
>
> Alex
>
>
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To: pgsql-performance@postgresql.org
Cc: havasvolgyi.otto@gmail.com
Subject: Re: Throwing unnecessary joins away
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