From: | David G Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: returning only part of a rule set |
Date: | 2014-11-25 22:24:57 |
Message-ID: | 1416954297056-5828226.post@n5.nabble.com |
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Lists: | pgsql-general |
Adrian Klaver-4 wrote
>>
>> If I am only interested in get 2 entries per result set, I would expect
>> to see
>
> Actually <=2.
> How do you determine which rows to keep, by id or something else?
>
>>
>> 1 xx,yy
>> 2 xx,yy
>>
>>
>> 1,dd,zz
>> 2,dd,zz
>>
>> 1, ee,ff
>>
>> Using LIMIT only gives
>> 1 xx,yy
>> 2 xx,yy
>>
>> Sorry for not explaining it very, I want to limit the size of an
>> inviduail set of records which is part of set of records.
>
> It would help if we could see the actual query you are using to get the
> result sets, suitably anonymized if needed.
The general answer is that you use a window clause and a row_number()
function over an appropriate partiton. Put that in a subquery then in the
outer query add a where clause for row_number <= 2.
David J.
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