From: David G Johnston <david.g.johnston@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Postgres does not use indexes with OR-conditions
Date: Fri, 7 Nov 2014 08:50:26 -0800 (PST)
Message-ID: <1415379026083-5826065.post@n5.nabble.com> (raw)
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Kevin Grittner-5 wrote
> Andrew Dunstan <
> andrew@
> > wrote:
>> On 11/07/2014 12:06 AM, Vlad Arkhipov wrote:
>
>>> I need to rewrite it in the way below to make Postgres use the index.
>>>
>>> select *
>>> from commons.financial_documents fd
>>> where fd.creation_time <= '2011-11-07 10:39:07.285022+08'
>>> and (
>>> fd.creation_time < '2011-11-07 10:39:07.285022+08'
>>> or (fd.creation_time = '2011-11-07 10:39:07.285022+08' and
>>> fd.financial_document_id < 100)
>>> )
>>> order by fd.creation_time desc
>>> limit 200
>>
>> Could you not rewrite it as something this?:
>>
>> where fd.creation_time <= '2011-11-07 10:39:07.285022+08'
>> and (fd.creation_time < '2011-11-07 10:39:07.285022+08'
>> or fd.financial_document_id < 100)
>
> Yeah, when there are two ways to write a query that are logically
> equivalent, it is better to put the AND at the higher level than
> the OR. On the other hand, why not simply write it as?:
>
> select *
> from commons.financial_documents fd
> where (fd.creation_time, fd.financial_document_id)
> < ('2011-11-07 10:39:07.285022+08', 100)
> order by fd.creation_time desc
> limit 200
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To: pgsql-performance@postgresql.org
Cc: david.g.johnston@gmail.com
Subject: Re: Postgres does not use indexes with OR-conditions
In-Reply-To: <1415379026083-5826065.post@n5.nabble.com>
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