Re: how to enforce index usage with +0

On Sun, Jun 10, 2007 at 05:32:55AM -0700, Timasmith wrote:
> select s.order_id
> from small_orders_table s, orders o
> where s.find_these_id in
>  (select some_id from some_table where some_indexed_field = 'ABC')
>  and s.order_id+0 = o.order_id
>  and date_trunc('microseconds', o.valid_until_dt) < now()
>
> This should essentially use the s.some_indexed_field as the primary
> index and hit the orders table on the order id.

It will do this automatically if the selectivity of your
some_indexed_field values leans that way.  I think you're probably
trying to outsmart the planner/optimiser here, and that's _usually_
not a good idea.  IT shouldn't make any difference whether you add
that +0 or not, assuming the database is tuned correctly.

I'd be rather more worried about the date_trunc stuff.  You probably
want a functional index on there.

A

--
Andrew Sullivan  | ajs@crankycanuck.ca
This work was visionary and imaginative, and goes to show that visionary
and imaginative work need not end up well.
        --Dennis Ritchie