SELECT Sid,AVG(score) FROM sc GROUP BY Sid;
SELECT Sid,AVG(score) AS avg FROM sc GROUP BY Sid HAVING avg >70;
SELECT s.Sid,s.Sname,avg FROM student AS s JOIN (SELECT Sid, AVG(score) AS avg FROM sc GROUP BY Sid HAVING avg >70) AS k ON s.Sid = k.Sid;
原文：https://www.cnblogs.com/zunfengliu/p/12198743.html