# 第08章_聚合函数课后练习

#1.where子句可否使用组函数进行过滤?  NO !

#2.查询公司员工工资的最大值，最小值，平均值，总和
SELECT MAX(salary) max_sal,MIN(salary) min_sal,AVG(salary) avg_sal,SUM(salary) sum_sal
FROM employees;

#3.查询各job_id的员工工资的最大值，最小值，平均值，总和
SELECT job_id,MAX(salary),MIN(salary),AVG(salary),SUM(salary)
FROM employees
GROUP BY job_id;

#4.选择具有各个job_id的员工人数
SELECT job_id,COUNT(*)
FROM employees
GROUP BY job_id;

# 5.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;

# 6.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)
FROM employees
WHERE manager_id IS NOT NULL
GROUP BY manager_id
HAVING MIN(salary) >= 6000;

# 7.查询所有部门的名字，location_id，员工数量和平均工资，并按平均工资降序
SELECT d.department_name,d.location_id,COUNT(employee_id),AVG(salary)
FROM employees e RIGHT JOIN departments d
ON e.department_id = d.department_id
GROUP BY department_name,location_id
ORDER BY AVG(salary) DESC;

SELECT employee_id,salary,department_name,location_id
FROM employees e RIGHT JOIN departments d
ON e.department_id = d.department_id;

# 8.查询每个工种、每个部门的部门名、工种名和最低工资
SELECT d.department_name,e.job_id,MIN(salary)
FROM employees e RIGHT JOIN departments d
ON e.department_id = d.department_id
GROUP BY job_id,department_name;