sql having的使用

id	teach_id	name	age
1	1	小红	13
2	1	小清	14
3	2	小d	11
4	1	小1	13
5	1	小2	14
6	2	小a	11

不使用having

SELECT * FROM (SELECT teach_id, AVG(age) AS age FROM student
 GROUP BY teach_id) t WHERE t.age > 12;

使用having

SELECT teach_id, AVG(age) AS age FROM student
 GROUP BY teach_id
HAVING AVG(age) > 12

having可以为分组设置条件