From: Alessandro Baretta <a.baretta@barettadeit.com>
To: Ottó Havasvölgyi <havasvolgyi.otto@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Throwing unnecessary joins away
Date: Thu, 12 Jan 2006 13:35:07 +0100
Message-ID: <43C64CFB.9030504@barettadeit.com> (raw)
In-Reply-To: <34608c0c0601120418n1af567b9n@mail.gmail.com>
References: <34608c0c0601120418n1af567b9n@mail.gmail.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: a.baretta@barettadeit.com, havasvolgyi.otto@gmail.com
Subject: Re: Throwing unnecessary joins away
In-Reply-To: <43C64CFB.9030504@barettadeit.com>
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