Re: Simple Join

Kevin Brown wrote:
> I'll just start by warning that I'm new-ish to postgresql.
>
> I'm running 8.1 installed from source on a Debian Sarge server. I have a
> simple query that I believe I've placed the indexes correctly for, and I
> still end up with a seq scan. It makes sense, kinda, but it should be able
> to use the index to gather the right values. I do have a production set of
> data inserted into the tables, so this is running realistically:
>
> dli=# explain analyze SELECT ordered_products.product_id
> dli-# FROM to_ship, ordered_products
> dli-# WHERE to_ship.ordered_product_id = ordered_products.id AND
> dli-# ordered_products.paid = TRUE AND
> dli-# ordered_products.suspended_sub = FALSE;

You scan 600000 rows from to_ship to get about 25000 - so some way to
cut this down would help.

Try out an explicit INNER JOIN which includes the filter info for paid
and suspended_sub in the join condition (you may need indexes on each of
id, paid and suspended_sub, so that the 8.1 optimizer can use a bitmap
scan):

SELECT ordered_products.product_id
FROM to_ship INNER JOIN ordered_products
ON (to_ship.ordered_product_id = ordered_products.id
AND ordered_products.paid = TRUE AND
ordered_products.suspended_sub = FALSE);