친구 수 집계하기WITH tmp AS (SELECT user_a_id AS user_id , user_b_id AS friend_idFROM edgesUNION ALLSELECT user_b_id AS user_id , user_a_id AS friend_idFROM edges)SELECT u.user_id , COUNT(DISTINCT t.friend_id) AS num_friendsFROM users AS uLEFT JOIN tmp AS t ON u.user_id = t.user_idGROUP BY u.user_idORDER BY num_friends DESC , user_id 작성 순서1. edges 테이블에서 1행의 데이터는 하나의 관계를 나타내지만, 이는 2명의 친구 정보를..