How do I structure a SQL query to find an object that is the parent of two specific other objects?

Question

Say I have 2 tables, called parent and child. A parent can have zero to many children, and a child can have 1 to many parents. How do I find all the parent elements that are par

Answer 1

You are looking for parents where two specific child records exist. Use the EXISTS clause for that:

SELECT *
FROM parent p
WHERE EXISTS (select * from join_table j where j.parent_id = p.id and j.child_id = 1)
  AND EXISTS (select * from join_table j where j.parent_id = p.id and j.child_id = 2);

Answer 2

An alternative to the accepted answer, probably faster:

SELECT p.*
FROM parent p JOIN join_table j ON p.id=j.parent_id
WHERE j.child_id=1 OR j.child_id=2
GROUP BY j.parent_id
HAVING COUNT(j.child_id)=2;