分组查询 - 《SQL》

GROUP BY
分组函数
添加筛选条件

查询邮箱中包含a字符的，每个部门的平均工资

SELECT
    avg(salary),
    department_id
from
    employees
    where
        email like('%a%')
    group by
        department_id;

分组前筛选：

例：
查询有奖金的每个领导手下员工的最高工资

#查询有奖金的每个领导手下员工的最高工资
SELECT
    MAX( salary ),
    manager_id 
FROM
    employees 
WHERE
    commission_pct 
GROUP BY
    manager_id;

分组后筛选
查询哪个部门的员工个数>2

SELECT
    count(*),
    department_id 
FROM
    employees 
GROUP BY
    department_id
HAVING
    COUNT(*)>2;