Is this the most efficient way to write this query? Id like to get a
list of users that have the categories 1, 2, and 3?
SELECT user_id FROM user_categories WHERE category_id IN (1,2,3) GROUP
BY user_id HAVING COUNT(*) = 3
users_categories (user_id, category_id)
1 | 1
1 | 2
1 | 3
2 | 1
2 | 2
3 | 1
4 | 1
4 | 2
4 | 3
The result should produce 1 & 4.