练习

#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job_id排序
SELECT
    MAX(salary),MIN(salary),AVG(salary),SUM(salary),job_id
FROM
    employees
GROUP BY
    job_id
ORDER BY
    job_id ASC;
#2.查询员工最高工资和最低工资的差距（difference）
SELECT
    MAX(salary)-MIN(salary) AS 差距
FROM
    employees;
#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
    MIN(salary),manager_id
FROM 
    employees
WHERE
    manager_id IS NOT NULL
GROUP BY
    manager_id
HAVING 
    MIN(salary) >= 6000
#4.查询所有部门的编号，员工数量和工资平均值，并按平均工资降序
SELECT 
    department_id,COUNT(*),AVG(salary)
FROM
    employees
GROUP BY
    department_id
ORDER BY
    AVG(salary) DESC;
#5.选择具有各个job_id的员工人数
SELECT
    COUNT(*),job_id
FROM
    employees
GROUP BY
    job_id;