Re: Handling large number of OR/IN conditions

A separate table for managing the relationships. One column for the manager
and one for employee.

Then you end up with a query like this.

Select field1,field2 FROM table1 inner join relationships on
table1.creator_user_id = relationships.employee WHERE relationships.manager
= ?

_____

From: pgsql-general-owner(at)postgresql(dot)org
[mailto:pgsql-general-owner(at)postgresql(dot)org] On Behalf Of David Wall
Sent: Friday, May 01, 2009 12:49 PM
To: pgsql-general(at)postgresql(dot)org
Subject: [GENERAL] Handling large number of OR/IN conditions

We have a database report function that seemed clean when the number of
users was small, but as the number of users grow, I was wondering if anybody
had any good ideas about how to handle OR or IN for SELECTs.

The general scenario is that a manager runs reports that list all records
that were created by users under his/her oversight. So, when the number of
users is small, we had simple queries like:

SELECT field1, field2 FROM table1 WHERE creator_user_id = 'U1' OR
creator_user_id = 'U2';

But when there are thousands of users, and a manager has oversight of 100 of
them, the OR construct seems out of whack when you read the query:

WHERE creator_user_id = 'U1' OR creator_user_id = 'U2' ... OR
creator_user_id = 'U99' OR creator_user_id = 'U100'

I know it can be shortened with IN using something like, but don't know if
it's any more/less efficient or a concern:

WHERE creator_user_id IN ('U1', 'U2', ...., 'U99', 'U100)

How do people tend to handle this sort of thing? I suspect manager reports
against their people must be pretty common. Are there any good tricks on
how to group users like this? Unfortunately, group membership changes over
time, and users may report to more than one manager and thus belong to more
than one group, so we can't just have a 'creator_group_id' attribute that is
set and then query against that.

Thanks,
David