| 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
