Question

我运行了以下代码，但NULL未显示在最终查询结果中。我可以看到NULL被插入临时表中。当我在查询中调用变量时，不会显示NULL值。

USE [AdventureWorks2014]; 
GO  

SET NOCOUNT ON; 
SET STATISTICS IO ON;  

DECLARE @values TABLE 
(     
 Value VARCHAR(MAX) NULL 
)  

INSERT INTO @values 
VALUES (NULL), ('Black'), ('Blue'), ('Grey'), ('Multi'), ('Red'), ('Silver'), ('Silver'), ('Black'), ('White'), ('Yellow')  --SELECT Value FROM @values; 

SELECT Production.Product.Name, Production.Product.ProductNumber,   Production.Product.Color, Production.Product.ListPrice,   Production.Product.SIZE, Production.Product.[Weight],   Production.Product.ProductLine, Production.Product.Class,   Production.Product.STYLE, Production.ProductPhoto.ThumbNailPhoto,   Production.ProductPhoto.LargePhoto FROM Production.Product INNER JOIN Production.ProductProductPhoto   ON Production.Product.ProductID =     Production.ProductProductPhoto.ProductID   INNER JOIN Production.ProductPhoto   ON Production.ProductProductPhoto.ProductPhotoID =     Production.ProductPhoto.ProductPhotoID 
--BEGIN CALLOUT A 
WHERE --Production.Product.Color IS NOT NULL 
(Production.Product.Color IN (SELECT Value FROM @values)); 
--END CALLOUT A 
GO

Answer 1

IN语句将与(field = val1) OR (field = val2) OR (field = val3)完全相同地执行。将NULL放在那里将归结为(field = NULL)，这自然不起作用。

不要将NULL插入@values，请尝试以下操作：

WHERE (Production.Product.Color IN (SELECT Value FROM @values))
   OR (Production.Product.Color IS NULL)

Answer 2

SET NOCOUNT ON; 
SET STATISTICS IO ON;  

DECLARE @values TABLE 
(     
 Value VARCHAR(MAX) NULL 
)  

INSERT INTO @values 
VALUES (NULL), ('Black'), ('Blue'), ('Grey'), ('Multi'), ('Red'), ('Silver'), ('Silver'), ('Black'), ('White'), ('Yellow')  --SELECT Value FROM @values; 

SELECT Production.Product.Name, Production.Product.ProductNumber,   Production.Product.Color, Production.Product.ListPrice,   Production.Product.SIZE, Production.Product.[Weight],   Production.Product.ProductLine, Production.Product.Class,   Production.Product.STYLE, Production.ProductPhoto.ThumbNailPhoto,   Production.ProductPhoto.LargePhoto 
FROM Production.Product 
INNER JOIN Production.ProductProductPhoto   ON Production.Product.ProductID =     Production.ProductProductPhoto.ProductID   
INNER JOIN Production.ProductPhoto   ON Production.ProductProductPhoto.ProductPhotoID =     Production.ProductPhoto.ProductPhotoID 
--BEGIN CALLOUT A 
WHERE --Production.Product.Color IS NOT NULL 
(ISNULL(Production.Product.Color,'EMPTY') IN (SELECT ISNULL(Value,'EMPTY') FROM @values)); 
--END CALLOUT A 
GO

Answer 3

使用INTERSECT

WHERE 
  exists (SELECT Production.Product.Color INTERSECT SELECT Value FROM @values)

表变量和NULLS

3 个答案: