1949. Strong Friendship (Medium).sql

WITH friends AS (
SELECT user1_id,user2_id
FROM friendship_1949
UNION
SELECT user2_id,user1_id
FROM friendship_1949
)
SELECTf1.user1_id,f2.user1_id,COUNT(f2.user1_id) AS num_mututal_friends
FROM friends f1
INNER JOIN friends f2 
ONf1.user1_id<>f2.user1_idANDf1.user2_id=f2.user2_id
WHEREf1.user1_id<f2.user1_id
GROUP BYf1.user1_id,f2.user1_id
HAVINGCOUNT(f2.user1_id) >=3