-- 1 查找出成绩表中所有学生的平均数
SELECT Sid,AVG(score) FROM sc GROUP BY Sid;
-- 2.查找出平均分数 大于70 avg(score) > 70;
SELECT Sid,AVG(score) AS avg FROM sc GROUP BY Sid HAVING avg >70;
-- 3.在学生表中获取Sid 和 sname字段 拼接 《平均分数 大于70》表中的 avg字段
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;