Find all users who rated all the movies rated by a specific user
This will not suffer from duplicate votes

SELECT user_id
FROM ratings 
WHERE movie_id IN (SELECT movie_id FROM ratings WHERE user_id = '1234') AND user_id &lt;&gt; '1234'
GROUP BY user_id 
HAVING count(DISTINCT movie_id) = (SELECT count(DISTINCT movie_id) FROM ratings WHERE user_id = '1234')