Date: Fri, 25 Feb 2011 01:03:12 +0100
From: Jochen Erwied <jochen@pgsql-performance.erwied.eu>
Organization: Creative Chaos Computing
Message-ID: <1923741490.20110225010312@erwied.eu>
To: Dave Crooke <dcrooke@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Possible parser bug? .... Re: Picking out the most recent row
	using a time stamp column
In-Reply-To: <AANLkTinaxt=xjbxOpXTeoL7SZ6dxJgEU8eDtp2dEbHKq@mail.gmail.com>
References: <AANLkTinaxt=xjbxOpXTeoL7SZ6dxJgEU8eDtp2dEbHKq@mail.gmail.com>
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Friday, February 25, 2011, 12:53:08 AM you wrote:

> select distinct on (a,    b,    c)
> a,   b c,   time_stamp,    value

Without the comma, you declare 'b AS c'

> from data
> order by a, b, c, time_stamp desc;

> The output produced is the same as this query:

> select distinct on (a,    b)
> a,   b,   time_stamp,    value
> from data
> order by a, b, time_stamp desc;

the 'c' is optimized away, since it is an alias for b, and thus redundant=
=20
for the distinct.

> Not sure if this is considered a parser bug or not, but it feels slightly
> odd not to get an error.

No error, just plain SQL :-)


--=20
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