SQL 中 HAVING 用法

现在 Student表有 如下数据

现需求如下： 查找每个老师的学生的平均年龄且平均年齿大于12

不使用 HAVING

 SELECT * FROM (SELECT TeacherID, AVG(Age) AS AGE FROM Student
   GROUP BY TeacherID) T WHERE T.AGE > 12

使用HAVING

   SELECT TeacherID, AVG(Age) AS AGE FROM Student
   GROUP BY TeacherID
   HAVING AVG(Age) > 12

结果如下：

HAVING:给分组设置条件