Question

我的if语句似乎永远不会做任何事情。我从ASP页面输入@active，并通过从Cots Table中选择CActive来设置@cactive。你们这个陈述有什么不对吗？它为什么不执行？我正在使用SQL Server 2005

//Declare Variables Here (about 20)

AS
If @currentdate is null
SET @currentdate = GETDATE()

Update Cots
SET //UPDATE ALL FIELDS HERE
Where CoID = @CID

SET @cactive =
(
Select CActive
From Cots
Where CoID = @CID
)

If @cactive != @active
Begin
INSERT INTO Activity
        (CoID,ActivityDate, ActivityName, ActivityNote, ActivityMediaContact, ActivityOwner)
        Values (@CID, @currentdate, 'Co ' + @fname + ' ' + @lname + 'made inactive','Co made inactive on ' + CAST(@currentdate AS varchar(50)), 'User', 'User')
End

INSERT INTO Activity
        (CoID,ActivityDate, ActivityName, ActivityNote, ActivityMediaContact, ActivityOwner)
        Values (@CID, @currentdate, 'Updated ' + @fname + ' ' + @lname,'Updated on ' + CAST(@currentdate AS varchar(50)), 'User', 'User')

Answer 1

如果其中任何一个为空，它们永远不会相等或不相等

If @cactive != @active

实施例

DECLARE @i int, @i2 int
IF @i <> @i2
PRINT 'not equal'

IF @i = @i2
PRINT 'equal'

使用ISNULL()/COALESCE()或IS NULL/IS NOT NULL

检查NULLS

Answer 2

使用IS NULL最适合检查条件，就像在WHERE子句中一样。

你应该使用ISNULL（）函数......

USE AdventureWorks2008R2;
GO
SELECT AVG(ISNULL(Weight, 50))
FROM Production.Product;
GO

SQL如果语句无法正常工作

2 个答案: