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* Create interval using column value?
@ 2004-10-25 02:54 Larry Lennhoff <llennhoff-postgres@pexicom.com>
0 siblings, 2 replies; 4+ messages in thread
From: Larry Lennhoff @ 2004-10-25 02:54 UTC (permalink / raw)
To: pgsql-sql
Hi
I have a table (A) with a integer column called build_interval, which
contains the number of milliseconds betweeen builds. I have another table
(B) with a timestamp with timezone column called built_on. The two tables
share a column called join_col. What I want to do is find all the rows in
A which were built before now() - build_interval seconds ago. If I could
just write this in SQL it would look something like:
SELECT A.id FROM A JOIN B ON (join_col) WHERE built_on < now() - interval
'build_interval seconds'; This does not work at all - I cannot find a way
to build an interval using a column - casting an integer as an interval is
forbidden. Can anyone suggest a way to achieve my desired result? I'm not
wedded to the interval approach. I can probably change the column type of
build_interval if necessary.
I am using postgres 7.3.4
Thanks in advance for any help.
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: Create interval using column value?
@ 2004-10-25 03:11 Tom Lane <tgl@sss.pgh.pa.us>
parent: Larry Lennhoff <llennhoff-postgres@pexicom.com>
1 sibling, 1 reply; 4+ messages in thread
From: Tom Lane @ 2004-10-25 03:11 UTC (permalink / raw)
To: Larry Lennhoff <llennhoff-postgres@pexicom.com>; +Cc: pgsql-sql
Larry Lennhoff <llennhoff-postgres@pexicom.com> writes:
> What I want to do is find all the rows in
> A which were built before now() - build_interval seconds ago. If I could
> just write this in SQL it would look something like:
> SELECT A.id FROM A JOIN B ON (join_col) WHERE built_on < now() - interval
> 'build_interval seconds';
You are confused about the difference between a literal constant and an
expression. Try something like
... WHERE built_on < now() - build_interval * interval '1 second';
which relies on the number-times-interval operator.
regards, tom lane
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: Create interval using column value?
@ 2004-10-25 03:13 Michael Glaesemann <grzm@myrealbox.com>
parent: Larry Lennhoff <llennhoff-postgres@pexicom.com>
1 sibling, 0 replies; 4+ messages in thread
From: Michael Glaesemann @ 2004-10-25 03:13 UTC (permalink / raw)
To: Larry Lennhoff <llennhoff-postgres@pexicom.com>; +Cc: pgsql-sql
On Oct 25, 2004, at 11:54 AM, Larry Lennhoff wrote:
> SELECT A.id FROM A JOIN B ON (join_col) WHERE built_on < now() -
> interval 'build_interval seconds';
It would help to see the error you're getting, but I suspect it has
something to do with the fact that you're quoting 'build_interval'. Try
something like WHERE built_on < current_timestamp - build_interval *
INTERVAL '0.001 second';
(btw, current_timestamp is the SQL standard for now() )
Regards,
Michael Glaesemann
grzm myrealbox com
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: Create interval using column value?
@ 2004-10-25 03:18 Larry Lennhoff <llennhoff-postgres@pexicom.com>
parent: Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 0 replies; 4+ messages in thread
From: Larry Lennhoff @ 2004-10-25 03:18 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; +Cc: pgsql-sql
Thanks, that was exactly what I needed.
Larry
]At 11:11 PM 10/24/2004, Tom Lane wrote:
>Larry Lennhoff <llennhoff-postgres@pexicom.com> writes:
> > What I want to do is find all the rows in
> > A which were built before now() - build_interval seconds ago. If I could
> > just write this in SQL it would look something like:
>
> > SELECT A.id FROM A JOIN B ON (join_col) WHERE built_on < now() - interval
> > 'build_interval seconds';
>
>You are confused about the difference between a literal constant and an
>expression. Try something like
>
>.. WHERE built_on < now() - build_interval * interval '1 second';
>
>which relies on the number-times-interval operator.
>
> regards, tom lane
^ permalink raw reply [nested|flat] 4+ messages in thread
end of thread, other threads:[~2004-10-25 03:18 UTC | newest]
Thread overview: 4+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2004-10-25 02:54 Create interval using column value? Larry Lennhoff <llennhoff-postgres@pexicom.com>
2004-10-25 03:11 ` Tom Lane <tgl@sss.pgh.pa.us>
2004-10-25 03:18 ` Larry Lennhoff <llennhoff-postgres@pexicom.com>
2004-10-25 03:13 ` Michael Glaesemann <grzm@myrealbox.com>
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