题解 | 查询成绩

WITH t AS (
    SELECT stu.sId
    FROM Student stu
    JOIN (SELECT sId, cId, score FROM SC GROUP BY sId, cId, score) sc ON stu.sId = sc.sId
    JOIN Course c ON sc.cId = c.cId
    WHERE cname IN ('语文', '数学', '英语')
    GROUP BY stu.sId
    HAVING AVG(sc.score) > 60
      AND COUNT(1) = 3
)
SELECT count(*)
FROM t

WHERE cname IN ('语文', '数学', '英语') 保证学科只为语文，数学，英语

HAVING AVG(sc.score) > 60 AND COUNT(1) = 3 保证3科的成绩的平均值大于60，防止缺科（但用例没覆盖这种场景）