MySQL - 基础题练习题 - 查询篇(4)

数据在本专栏的第一篇博客里

本篇考察分组查询

5.1.查询各job_id的员工工资的最大值、最小值、平均值、总和，并按照job_id升序

SELECT
	MAX( salary ),
	MIN( salary ),
	AVG( salary ),
	SUM( salary ) 
FROM
	employees 
GROUP BY
	job_id 
ORDER BY
	job_id ASC;

5.2.查询员工最高工资和最低工资的差距（difference）

SELECT
	(
	MAX( salary )- MIN( salary )) AS difference 
FROM
	employees;

5.3.查询各个管理者手下员工的最低工资，其中最低工资不能低于6000， 没有管理者的员工不计算在内

SELECT
	manager_id,
	MIN( salary ) AS m 
FROM
	employees 
WHERE
	manager_id 
GROUP BY
	manager_id 
HAVING
	m >= 6000;

5.4.查询所有部门的编号，员工数量和工资平均值，并按照平均工资降序

SELECT
	department_id,
	COUNT(*),
	AVG( salary ) AS a 
FROM
	employees 
GROUP BY
	department_id 
ORDER BY
	a DESC;

5.5.选择具有各个job_id的员工人数

SELECT
	job_id,
	count(*) 
FROM
	employees 
GROUP BY
	job_id;