How to filter SQL results in a has-many-through relation

Question

Assuming I have the tables student, club, and student_club:

student {
    id
    name
}
club {
    id
    name
}
stude         


        

Answer 1

So there's more than one way to skin a cat.
I'll to add two more to make it, well, more complete.

1) GROUP first, JOIN later

Assuming a sane data model where (student_id, club_id) is unique in student_club. Martin Smith's second version is like somewhat similar, but he joins first, groups later. This should be faster:

SELECT s.id, s.name
  FROM student s
  JOIN (
   SELECT student_id
     FROM student_club
    WHERE club_id IN (30, 50)
    GROUP BY 1
   HAVING COUNT(*) > 1
       ) sc USING (student_id);

2) EXISTS

And of course, there is the classic EXISTS. Similar to Derek's variant with IN. Simple and fast. (In MySQL, this should be quite a bit faster than the variant with IN):

SELECT s.id, s.name
  FROM student s
 WHERE EXISTS (SELECT 1 FROM student_club
               WHERE  student_id = s.student_id AND club_id = 30)
   AND EXISTS (SELECT 1 FROM student_club
               WHERE  student_id = s.student_id AND club_id = 50);