解读在SQL Server中处理空值时涉及的三个问题_Mssql数据库教程

以下为引用的内容：

SET NOCOUNT ON

GO

CREATE TABLE xCount

(pkey1 INT IDENTITY NOT NULL

CONSTRAINT pk_xCount PRIMARY KEY,

Col1 int NULL)

GO
INSERT xCount (Col1) VALUES (10)

GO

INSERT xCount (Col1) VALUES (15)

GO
INSERT xCount (Col1) VALUES (20)

GO

INSERT xCount (Col1) VALUES (NULL)

GO

SELECT AVG(Col1) AvgWithoutIsNullFunctionOnCol1,

AVG(ISNULL(Col1,0)) AvgWithIsNullFunctionOnCol1,

COUNT(Col1) NoIsNullFunctionOnCol1 ,

COUNT(ISNULL(Col1,0)) UsingIsNullFunctionOnCol1,

Count(*) UsingAsterisk

FROM xCount

GO

DROP TABLE xCount

GO

OUTPUT:

AvgWOIsNullFnctnCol1 AvgWIsNullFnctnCol1 WOIsNullFnctnCol1

WIsNullFnctnCol1 UsingAsterisk

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

15 11 3 4 4

以下为引用的内容：

SET NOCOUNT ON

GOCREATE TABLE Parent(pkey1 INT IDENTITY NOT NULL

CONSTRAINT pkParent PRIMARY KEY,col1 INT NULL)GOINSERT

Parent (col1) VALUES (284)GOINSERT

Parent (col1) VALUES (326)GO