Re: how to make this database / query faster

On Sat, Mar 15, 2008 at 5:04 PM, brian <brian(at)zijn-digital(dot)com> wrote:

> As there's an index on id would it be faster to transpose the WHERE
> conditions?
>
> WHERE id > your_last_id
> AND session_key IS NOT NULL
>
> I can't remember if the order of WHERE is significant.
>

I don't think that the order of WHERE clause conditions are significant with
PostgreSQL since it has a sophisticated planner. One way to be sure would
be to examine the EXPLAIN plans for different where clause ordering to see
if the query plan changes depending upon the order specified.

Another way to make this query faster would be to create a partial index on
id;

CREATE UNIQUE INDEX Partial_id
ON Users
WHERE session_key IS NOT NULL;

This index would be much smaller if there are many session_keys that are
null, so it should be loaded as searched much faster.