Question

I have one table that I need to bump against multiple tables with left outer joins excluding the right(s). Is there a best practice for this? Union all the other tables first? Something else?

Here’s the first thought that comes to my mind to handle this, but I want to know if there is a better more efficient way.

select
    master_table.*
from
    master_table
left outer join
    (
        select customer_id from table_1
        union
        select customer_id from table_2
        union
        select customer_id from table_3
        union
        select customer_id from table_4
    ) bump_table
on
    master_table.customer_id = bump_table.customer_id
where
    bump_table.customer_id is null

Answer 1

I should think a NOT EXISTS would be better. It certainly better communicates the intent of the query.

select * from master_table m
 where not exists( select 1 from table_1 where m.customer_id=table_1.customer_id)
   and not exists( select 1 from table_2 where m.customer_id=table_2.customer_id)
   and not exists( select 1 from table_3 where m.customer_id=table_3.customer_id)
   and not exists( select 1 from table_4 where m.customer_id=table_4.customer_id)