Question

下面是查询，当不使用convert to varchar时返回0。比较整数值

SELECT 
    *,
    CASE 
       WHEN Duration IS NULL
          THEN CONVERT(VARCHAR, '') 
          ELSE Duration 
    END AS Duration  
FROM
    Contribution 
WHERE 
    CreatedBy = @in_userID  AND ContentStatus = @ContentStatus   

UNION ALL

SELECT 
    *,
    CASE 
       WHEN Duration IS NULL
          THEN CONVERT(VARCHAR, '')  
          ELSE Duration 
    END AS Duration  
FROM
    Training  
WHERE 
    CreatedBy = @in_userID  AND ContentStatusValue = @TrainingStatus

使用全部并集时，不使用转换，大小写将返回0而不是“使用转换时，问题已解决。

有人可以说为什么会这样吗？

Answer 1

我怀疑您的Duration类型为INT，因此您可以进行对话：

SELECT c.col1, c.col2, ISNULL(CAST(c.Duration AS VARCHAR(255)),'') Duration  
FROM Contribution c
WHERE c.CreatedBy = @in_userID  AND
      c.ContentStatus = @ContentStatus 
UNION ALL
SELECT t.col1, t.col2, ISNULL(CAST(t.Duration AS VARCHAR(255), '') 
FROM Training t 
WHERE t.CreatedBy = @in_userID AND
      t.ContentStatusValue = @TrainingStatus;

Answer 2

您还可以使用COALESCE

SELECT *,COALESCE(convert( varchar(255),Duration ),'') 
AS Duration  FROM Contribution WHERE CreatedBy = @in_userID 
and ContentStatus = @ContentStatus   
UNION ALL

SELECT *,COALESCE(convert( varchar(255),Duration ),'') AS Duration 
FROM Training  WHERE CreatedBy = @in_userID  
and   ContentStatusValue=@TrainingStatus.

SQL Server：情况表达式返回0而不是空字符串

2 个答案: