Re: Queries not always using index on timestamp search - Mailing list pgsql-general

From Richard Huxton
Subject Re: Queries not always using index on timestamp search
Date
Msg-id 40DAFBB2.4090202@archonet.com
Whole thread Raw
In response to Queries not always using index on timestamp search  (Mike Nolan <nolan@gw.tssi.com>)
List pgsql-general
Mike Nolan wrote:
> Here are two queries (under 7.4.1):
>
> 'mytime' is a timestamp field that is indexed.
>
> select * from mytable where mytime > '2004-06-21'
>
> select * from mytable where mytime > current_date-3
>
> Looking at an explain on these queries, the first one will use the
> index and the second one will not, even though 'current_date-3'
> produces the same date as the hard-coded one in the first search.
>
> Is there a way to get the second query to use the index?

Probably the simplest is to define a function ago(int) that does the
calculation for you. Mark the function STABLE and that should do it. See
the archives for more discussion of this.


--
   Richard Huxton
   Archonet Ltd

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