Re: Postgres does not use indexes with OR-conditions

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On 11/07/2014 12:06 AM, Vlad Arkhipov wrote:
It was just a minimal example. The real query looks like this.

select *
from commons.financial_documents fd
where 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

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


First, please do not top-post on the PostgreSQL lists. See <http://idallen.com/topposting.html>

Second, the last test for fd.creation_time in your query seems redundant. 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)

cheers

andrew


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