mysql 筛选后分组查询

语法:
select 分组函数，列（要求出现在group by的后面）
from 表
where ..
group by 分组的列表
order by ...

#案例：查询各个部门的平均工资

SELECT AVG(salary),department_idFROM employeesGROUP BY    department_idORDER BY    department_id DESC;

#案例:查询每个工种的最高工资

SELECT    MAX(salary),job_idFROM    employeesGROUP BY    job_id;

#案例:查询每个部门的位置个数

SELECT    COUNT(location_id),department_nameFROM    departmentsGROUP BY    department_name;

#案例:查询邮箱中包含a字符的，每个部门的平均工资

SELECT    AVG(salary),department_idFROM    employeesWHERE    email LIKE('%a%')GROUP BY    department_id;

#案例：查询有奖金的每个领导手下员工的最高工资

SELECT    MAX(salary),manager_idFROM     employeesWHERE    commission_pct IS NOT NULLGROUP BY     manager_id;