From: Aaron Bono <postgresql@aranya.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Postgres SQL language list <pgsql-sql@postgresql.org>
Subject: Re: Unions and Grouping
Date: Fri, 15 Dec 2006 16:17:20 -0600
Message-ID: <bf05e51c0612151417o1bdfa65bh5e869185469f46e1@mail.gmail.com> (raw)
In-Reply-To: <21818.1166218924@sss.pgh.pa.us>
References: <bf05e51c0612151315s59e6647etc2dd45e940d41a2a@mail.gmail.com>
<21818.1166218924@sss.pgh.pa.us>
On 12/15/06, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> "Aaron Bono" <postgresql@aranya.com> writes:
> > My question, what do the SQL Specifications say should happen on a
> Union?
> > Is it supposed to eliminate duplicates even WITHIN the individual
> queries
> > that are being unioned?
>
> Yes. SQL92 7.10 saith:
>
> b) If a set operator is specified, then the result of applying
> the set operator is a table containing the following rows:
>
> i) Let R be a row that is a duplicate of some row in T1 or
> of
> some row in T2 or both. Let m be the number of duplicates
> of R in T1 and let n be the number of duplicates of R in
> T2, where m >= 0 and n >= 0.
>
> ii) If ALL is not specified, then
>
> Case:
>
> 1) If UNION is specified, then
>
> Case:
>
> A) If m > 0 or n > 0, then T contains exactly one
> dupli-
> cate of R.
>
> B) Otherwise, T contains no duplicate of R.
>
>
> regards, tom lane
>
So if I don't want the duplicated WITHIN the two queries to be eliminated, I
use UNION ALL?
Thanks!
--
==================================================================
Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.comhttp://codeelixir.com
==================================================================
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To: pgsql-sql@postgresql.org
Cc: postgresql@aranya.com, tgl@sss.pgh.pa.us
Subject: Re: Unions and Grouping
In-Reply-To: <bf05e51c0612151417o1bdfa65bh5e869185469f46e1@mail.gmail.com>
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