平均通过

Question

我有一个表调用部门提供柱： DepartmentID的 DepartmentName的

另一个表中调用EMPLOYEE使用列： EmployeeID为 DepartmentID的 EmployeeName 薪酬

我需要一个JOIN查询可能Group By显示DepartmentName和AVERAGE工资

基本上输出应显示： DepartmentX 40000 DepartmentY 15000 DepartmmentZ 35000

Answer 1

您需要使用AVG()聚合函数JOIN两个表之间像

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）获得平均，然后再执行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;