MySQL聚合函数练习

1.where子句可否使用组函数进行过滤? 
不能使用where子句，应该使用having子句
2.查询公司员工工资的最大值，最小值，平均值，总和 

SELECT MIN(salary),MAX(salary),SUM(salary),AVG(salary)
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,MIN(salary),MAX(salary),SUM(salary),AVG(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),MAX(salary)-MIN(salary) 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 department_name,location_id,COUNT(d.department_id),AVG(salary),SUM(salary)
FROM employees e RIGHT JOIN departments d
ON e.`department_id`=d.`department_id`
GROUP BY department_name,location_id
ORDER BY SUM(salary) DESC;

8.查询每个工种、每个部门的部门名、工种名和最低工资
 

SELECT job_id,d.department_id,department_name,MIN(salary)
FROM employees e LEFT JOIN departments d
ON e.`department_id`=d.`department_id`
GROUP BY job_id,department_id;