Question

I have two queries that I want to join together, but I don’t know how to.

Select father, mother, guardian from students where user_id = '201209291';

I get a result of 3 IDs.

Now, I need to use those three IDs to get their personal information;

Select * from system_users where user_id = (The 3 IDs from the previous query);

How would i go about solving this problem? I thought of the result of the first query into 3 rows, but I don’t know how to do that either.

Answer 1

Well, you can join directly using a series of ORs in the join predicate, as long as the father, mother, and guardian columns are actually user_ids in system_users.

select usrs.*
from students s 
join system_users usrs on 
    s.father=usrs.user_id OR
    s.mother=usrs.user_id OR
    s.guardian=usrs.user_id
where s.user_id = '201209291';