--三种方法查询人所在部门平均工资

--建表

IF OBJECT_ID(N‘Emp‘,‘U‘) IS NOT NULL

BEGIN

PRINT ‘This table have been existed‘;

END

ELSE

BEGIN

CREATE TABLE [dbo].[Emp]

(

[Name]       NVARCHAR(50) ,

[Slary]      INT,

[DepID]      INT

)

INSERT INTO [Emp]

SELECT N‘张三‘, ‘100‘, 1

UNION ALL

SELECT N‘李四‘, ‘200‘, 1

UNION ALL

SELECT N‘王五‘, ‘200‘, 2

UNION ALL

SELECT N‘张麻子‘, ‘300‘, 2

UNION ALL

SELECT N‘一柱擎天‘, ‘300‘, 2

UNION ALL

SELECT N‘陈勃‘, ‘400‘, 3

END

-------------------------------------------------------------------------------------------------------------------------

--方法:Nested Loop

SELECT a.*,(SELECT AVG(Slary) FROM [Emp] b WHERE b.DepID=a.DepID )

FROM [Emp] a

--方法:开窗

SELECT *, AVG(Slary) OVER(PARTITION BY DepID)

FROM [Emp]

--方法:

SELECT a.*, b.Avg

FROM [Emp] a INNER JOIN (SELECT DepID, AVG(Slary) Avg FROM [Emp] GROUP BY DepID) b ON a.DepID=b.DepID