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* Do cast affects index usage?
@ 2012-10-12 20:05 Anibal David Acosta <aa@devshock.com>
0 siblings, 2 replies; 5+ messages in thread
From: Anibal David Acosta @ 2012-10-12 20:05 UTC (permalink / raw)
To: pgsql-performance
I have a table with a column of type timestamp with time zone, this column
has an index
If I do a select like this
select * from mytable where cast(my_date as timestamp without time zone) >
'2012-10-12 20:00:00'
this query will use the index over the my_date column?
Thanks
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Do cast affects index usage?
@ 2012-10-12 20:37 Scott Marlowe <scott.marlowe@gmail.com>
parent: Anibal David Acosta <aa@devshock.com>
1 sibling, 0 replies; 5+ messages in thread
From: Scott Marlowe @ 2012-10-12 20:37 UTC (permalink / raw)
To: Anibal David Acosta <aa@devshock.com>; +Cc: pgsql-performance
On Fri, Oct 12, 2012 at 2:05 PM, Anibal David Acosta <aa@devshock.com> wrote:
> I have a table with a column of type timestamp with time zone, this column
> has an index
>
> If I do a select like this
>
> select * from mytable where cast(my_date as timestamp without time zone) >
> '2012-10-12 20:00:00'
>
> this query will use the index over the my_date column?
No. but it will use a functional index:
create index yada on blah (cast(my_date as timestaqmp without time zone));
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Do cast affects index usage?
@ 2012-10-12 20:38 Tom Lane <tgl@sss.pgh.pa.us>
parent: Anibal David Acosta <aa@devshock.com>
1 sibling, 1 reply; 5+ messages in thread
From: Tom Lane @ 2012-10-12 20:38 UTC (permalink / raw)
To: Anibal David Acosta <aa@devshock.com>; +Cc: pgsql-performance
"Anibal David Acosta" <aa@devshock.com> writes:
> I have a table with a column of type timestamp with time zone, this column
> has an index
> If I do a select like this
> select * from mytable where cast(my_date as timestamp without time zone) >
> '2012-10-12 20:00:00'
> this query will use the index over the my_date column?
No. The cast seems rather pointless though ...
regards, tom lane
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Do cast affects index usage?
@ 2012-10-13 00:27 Anibal David Acosta <aa@devshock.com>
parent: Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 5+ messages in thread
From: Anibal David Acosta @ 2012-10-13 00:27 UTC (permalink / raw)
To: 'Tom Lane' <tgl@sss.pgh.pa.us>; +Cc: pgsql-performance
Because I need to get all rows where datetime is greater than (for example)
'2012-10-10 00:00:00' but ignoring timezone, so basically I need to truncate
timezone
This can be done by converting to timestamp without timezone.
-----Mensaje original-----
De: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Enviado el: viernes, 12 de octubre de 2012 05:39 p.m.
Para: Anibal David Acosta
CC: pgsql-performance@postgresql.org
Asunto: Re: [PERFORM] Do cast affects index usage?
"Anibal David Acosta" <aa@devshock.com> writes:
> I have a table with a column of type timestamp with time zone, this
> column has an index
> If I do a select like this
> select * from mytable where cast(my_date as timestamp without time
> zone) >
> '2012-10-12 20:00:00'
> this query will use the index over the my_date column?
No. The cast seems rather pointless though ...
regards, tom lane
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Do cast affects index usage?
@ 2012-10-13 01:34 Tom Lane <tgl@sss.pgh.pa.us>
parent: Anibal David Acosta <aa@devshock.com>
0 siblings, 0 replies; 5+ messages in thread
From: Tom Lane @ 2012-10-13 01:34 UTC (permalink / raw)
To: Anibal David Acosta <aa@devshock.com>; +Cc: pgsql-performance
"Anibal David Acosta" <aa@devshock.com> writes:
> Because I need to get all rows where datetime is greater than (for example)
> '2012-10-10 00:00:00' but ignoring timezone, so basically I need to truncate
> timezone
> This can be done by converting to timestamp without timezone.
[ shrug... ] It can also be done without that. Whatever your cutoff
time is can be expressed as a timestamp *with* tz.
regards, tom lane
^ permalink raw reply [nested|flat] 5+ messages in thread
end of thread, other threads:[~2012-10-13 01:34 UTC | newest]
Thread overview: 5+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2012-10-12 20:05 Do cast affects index usage? Anibal David Acosta <aa@devshock.com>
2012-10-12 20:37 ` Scott Marlowe <scott.marlowe@gmail.com>
2012-10-12 20:38 ` Tom Lane <tgl@sss.pgh.pa.us>
2012-10-13 00:27 ` Anibal David Acosta <aa@devshock.com>
2012-10-13 01:34 ` Tom Lane <tgl@sss.pgh.pa.us>
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