Question

I have struggle to produce good SQL.
It is a relationship part of application.
I have 3 tables : users(‘id’), relationship(‘user_id’, ‘member_id’), relationship_block(‘user_id’, ‘blocked_member_id’)

I would like to get all members belonging to user with user_id that are not blocked.

Records of first table ‘users’ that are in ‘relationships’ table but that are NOT in ‘relationship_blocked’ table.
First 2 i can do with JOIN, but then I want to remove those that are blocked.

Thanx.

edit: found a good info about it here: http://explainextended.com/2010/05/27/left-join-is-null-vs-not-in-vs-not-exists-nullable-columns/

Answer 1

select *
    from users u
        inner join relationship r
            on u.user_id = r.user_id
        left join relationship_block rb
            on r.user_id = rb.user_id
                and r.member_id = rb.blocked_member_id
    where rb.user_id is null