MySQL Query to find customers who have ordered two specific products

Question

I\'m having trouble coming up with a query that will find all customers who have purchased both PROD1 and PROD2.

Here\'s a pseudo-query that kind of looks like what

Answer 1

SELECT userid
  FROM TRANSACTIONS
 WHERE product_id in ('prod1', 'prod2')
GROUP BY userid
HAVING COUNT(DISTINCT product_id) = 2