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From: Pavel Stehule <pavel.stehule@gmail.com>
To: Lee Hachadoorian <lee.hachadoorian@gmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: LIMIT BASED ON PERCENT
Date: Wed, 18 Nov 2009 20:39:34 +0100
Message-ID: <162867790911181139s38dd9ae4n7b1474523d3f2c3b@mail.gmail.com> (raw)
In-Reply-To: <5ab13580911181133k6204bbb0h33a695e618bfa02b@mail.gmail.com>
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	<200911182027.08857.guillaume@lelarge.info>
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	<5ab13580911181133k6204bbb0h33a695e618bfa02b@mail.gmail.com>

2009/11/18 Lee Hachadoorian <lee.hachadoorian@gmail.com>:
> On Wed, Nov 18, 2009 at 2:30 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
>> yes, and don't use 20%.
>>
>> select * from foo order by somecol limit (select (count(*)*0.2)::int from foo)
>>
>> Regards
>> Pavel
>
> Is this faster on a large table? Because (select (count(*)*20/100)) worked fine.
>

this is +/- same - 20/100 is maybe about 0.000001% faster - you don't
need one float to query cast, but this operation is only one pqr
query. The problem is two  full scan of table.

Pavel

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