From: Richard Huxton <dev@archonet.com>
To: Wei Weng <wweng@kencast.com>
To: pgsql-sql@postgresql.org
Subject: Re: How do you write this query?
Date: Thu, 31 Oct 2002 19:09:11 +0000
Message-ID: <200210311909.11341.dev@archonet.com> (raw)
In-Reply-To: <1036088486.13986.19.camel@Monet>
References: <1036088486.13986.19.camel@Monet>
On Thursday 31 Oct 2002 6:21 pm, Wei Weng wrote:
> data | data1 | data2
> ------+-------+-------
> 1 | foo | bar
> 2 | greg | bar
> 3 | pooh | bar
> 4 | dah | peng
>
> I need a query that returns me the "data1" that satisfies the logic of
> the following pseudo code:
>
> 1: select data2 into @out from test where data1 = 'pooh'
> 2: select data1 from test where data2 = @out and data = 3
The most literal would be something like:
SELECT t1.data1 FROM test t1
WHERE t1.data=3 AND t1.data2 IN
(SELECT t2.data2
FROM test t2
WHERE t2.data1='pooh')
You can probably get away without the t1/t2 stuff but that should make things
clear.
Since Postgresql isn't very good at optimising IN, you might want to rewrite
it as an EXISTS query instead - see the manuals and mailing list archives for
details.
HTH
--
Richard Huxton
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To: pgsql-sql@postgresql.org
Cc: dev@archonet.com, wweng@kencast.com
Subject: Re: How do you write this query?
In-Reply-To: <200210311909.11341.dev@archonet.com>
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