How can I do a left join but with two clauses

Question

I have two tables called listings and listings_queue. They are identical in structure. The idea is that records get put in the queue, stuff is done to them, and then they're moved to listings.

I want to run a query that pulls any record that exists in listings but not in listings_queue. The criteria for not existing is that it doesn't have the field mls_listing_id and mls_id that match any in listings_queue.

In plain english, "Give me any record in listings that doesn't have a record in listings_queue with the same mls_id AND mls_listing_id.

I've tried doing where clauses but can't get it to work.

Answer 1

Here is a way you can do this with a where clause:

select l.*
from listings l
where not exists (select 1
                  from listings_queue lq
                  where lq.mis_id = l.mis_id and lq.mis_listing_id = l.mis_listing_id
                 );

You can also do this as a left outer join:

select l.*
from listings l left outer join
     listings_queue lq
     on lq.mis_id = l.mis_id and lq.mis_listing_id = l.mis_listing_id
where lq.mis_id is null;

This could produce duplicates if the listings_queue table has multiple matches.