[에러해결] ERROR 1055 (42000) at line 1: Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column

ERROR 1055 (42000) at line 1: Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column

SQL 표준문법을 지키지 않아 생긴 문제, GROUP BY를 이용할 때 COUNT 외의 칼럼을 모두 기입해야한다.

SELECT H.hacke_id, H.name, COUNT(*) AS CNT
FROM Hackers ArS H
    JOIN Challenges AS C
    ON H.hacker_id = C.hacker_id
--- H.name의 추가가 필요하다. ---
GROUP BY H.hacker_id