SELECT數據查詢例題4——分組查詢

#1、查詢各job_id的員工工資的最大值，最小值，平均值，總和，並按job_id升序
SELECT MAX(salary),MIN(salary),AVG(salary),SUM(salary),job_id
FROM employees
GROUP BY job_id
ORDER BY job_id;


#2、查詢員工最高工資和最低工資的差距(DIFFERNCE)
SELECT MAX(salary)-MIN(salary) DIFFERNCE
FROM employees;


#3、查詢各個管理者手下員工的最低工資，其中最低工資不能低於6000，沒有管理者的員工不計算在內
SELECT MIN(salary),manager_id
FROM employees
WHERE manager_id IS NOT NULL
GROUP BY manager_id
HAVING MIN(salary)>=6000;

#4、查詢所以部門的編號，員工數量和工資平均值，並按平均值降序
SELECT department_id,COUNT(*),AVG(salary) a
FROM employees
GROUP BY department_id
ORDER BY a DESC;

#5、選擇具有各個job_id的員工人數
SELECT COUNT(*) 個數,job_id
FROM employees
GROUP BY job_id;