From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ozer, Pam <pozer@automotive.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Random sort with distinct
Date: Sat, 02 Oct 2010 09:52:50 -0400
Message-ID: <5070.1286027570@sss.pgh.pa.us> (raw)
In-Reply-To: <216FFB77CBFAEE4B8EE4DF0A939FF1D10182C8@mail-001.corp.automotive.com>
References: <216FFB77CBFAEE4B8EE4DF0A939FF1D10182C8@mail-001.corp.automotive.com>
"Ozer, Pam" <pozer@automotive.com> writes:
> Select Distinct VehicleMake, VehicleModel
> From VehicleYearMakeModelTrim
> Order by random()
> Limit 10;
> I don't want to bring back the random number I just want the sort order
> to be random. How can I sort randomly? This query breaks because
> random() is not in the select.
Well, yeah: the implication of the ORDER BY is that a new random value
is to be computed for each row of VehicleYearMakeModelTrim. After you
combine rows with DISTINCT it's not clear which of those values should
be used to sort a grouped row.
You need to put the DISTINCT and the ORDER BY in separate query levels,
like this:
select * from
(Select Distinct VehicleMake, VehicleModel
From VehicleYearMakeModelTrim) ss
Order by random()
Limit 10;
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, pozer@automotive.com
Subject: Re: Random sort with distinct
In-Reply-To: <5070.1286027570@sss.pgh.pa.us>
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