平均通過

Question

我有一個表調用部門提供柱： DepartmentID的 DepartmentName的

另一個表中調用EMPLOYEE使用列： EmployeeID爲 DepartmentID的 EmployeeName 薪酬

我需要一個JOIN查詢可能Group By顯示DepartmentName和AVERAGE工資

基本上輸出應顯示： DepartmentX 40000 DepartmentY 15000 DepartmmentZ 35000

Answer 1

您需要使用AVG()聚合函數JOIN兩個表之間像

SELECT d.DepartmentName, 
AVG(e.Salary) as average_salary 
FROM Employee e 
JOIN DEPARTMENTS d ON e.DepartmentID = d.DepartmentID 
GROUP BY e.DepartmentID; 

（OR）獲得平均，然後再執行JOIN像

SELECT d.DepartmentName, 
xx.average_salary 
FROM DEPARTMENTS d 
JOIN (
select DepartmentID, AVG(Salary) as average_salary 
from Employee 
GROUP BY DepartmentID) xx ON xx.DepartmentID = d.DepartmentID;