A query with primary key field used twice

问题

In my database I have two tables:

relationship table: organization_id_first, organization_id_second, relationship_type

organization table: primary key = org_id ; org_id, org_name, ...

How would I be able to join the organization table so that I could get the org_name for both organizations that have an entry in the relationship table? I don't think I can join on the same primary key. Would I have to do a subquery of some sort?

Thanks!

回答1:

This is how i would do it in T-SQL ... just join it twice and make two different object

select or1.org_name, or2.org_name, rel.relationship_type from relationship  rel
   join organization  or1 on rel.organization_id_first = or1.org_id
   join organization  or2 on rel.organization_id_second = or2.org_id

来源：https://stackoverflow.com/questions/35557789/a-query-with-primary-key-field-used-twice