Re: calculated expressions and index use

A very dirty work around could be:
select * from foo where created+at >= (select now() - '1 hour'::interval);

Or perhaps this already works:
select * from foo where created+at >= (now() - '1 hour'::interval);

Pavel Hlavnicka wrote:
> Hi all,
>
> I use simple sql statement like this
>
> select * from foo
> where created_at >= 'now'::timestamp - '1 hour'::interval;
>
> My table is indexed on created_at field. The query above doesn't use it,
> but if I use
>
> select * from foo where created_at >= 'now'
>
> the index is used.
>
> It looks like if the engine finds some expression to be evaluated it
> gets rid of any index use (due the possible dependency?).
>
> Is it possible to do something to 'precompute' some value in the query
> condition, so planner understand is as a constant value?
>
> (... and I've got some reason NOT to use a parameter in my Perl DBI code...)
>
> Maybe my conclusions are wrong, of course.
>
> Thank you very much in advance
>
> Pavel
>