Question

SELECT Id 
FROM dbo.OWL_AddlDataFields 
WHERE CustomerId = @BaseCustomerId 
  AND AddlDataFieldCategoryId = @AddlDataFieldCategoryId 
  AND AddlDataFieldGroupId = CASE 
                                WHEN @AddlDataFieldGroupId =  0 THEN  NULL 
                                ELSE  @AddlDataFieldGroupId 
                             END  
  AND Name = @DataFieldName

上述查询不会返回任何结果。我认为以上查询存在“AddlDataFieldCategoryId =＆＃39;和案件中的空。任何人都可以更正查询吗？

Answer 1

CASE表达式的问题在于您使用equals运算符将列与谓词进行比较，该谓词可能是NULL。这不会像预期的那样表现，因为NULL比较应该使用IS NULL而不是等于。一种可能的解决方法是将AddlDataFieldGroupId合并为数值。然后，我们可以确定CASE表达式只会将一个数字与另一个数字进行比较。

WHERE ... AND
COALESCE(AddlDataFieldGroupId, 0) = CASE WHEN 
                    @AddlDataFieldGroupId =  0
                                         THEN 0 ELSE  @AddlDataFieldGroupId END

Answer 2

如果AddlDataFieldGroupId不能为零，那么您根本不需要CASE。这将完成这项工作：

SELECT Id 
FROM dbo.OWL_AddlDataFields 
WHERE CustomerId = @BaseCustomerId 
AND AddlDataFieldCategoryId = @AddlDataFieldCategoryId 
AND AddlDataFieldGroupId = @AddlDataFieldGroupId
AND Name = @DataFieldName

如果AddlDataFieldGroupId可以为零，但不能为负数，则可以执行以下操作：

SELECT Id 
FROM dbo.OWL_AddlDataFields 
WHERE CustomerId = @BaseCustomerId 
AND AddlDataFieldCategoryId = @AddlDataFieldCategoryId 
AND AddlDataFieldGroupId = CASE WHEN 
@AddlDataFieldGroupId =  0 THEN -1 ELSE @AddlDataFieldGroupId END  
AND Name = @DataFieldName

或者，无论AddlDataFieldGroupId是什么，这都可行：

SELECT Id 
FROM dbo.OWL_AddlDataFields 
WHERE CustomerId = @BaseCustomerId 
AND AddlDataFieldCategoryId = @AddlDataFieldCategoryId 
AND AddlDataFieldGroupId = CASE WHEN 
@AddlDataFieldGroupId =  0 THEN AddlDataFieldGroupId - 1 ELSE @AddlDataFieldGroupId END  
AND Name = @DataFieldName

注意：所有这些解决方案均假设AddlDataFieldGroupId不能为NULL。

在sql中使用case null的问题

2 个答案: