在SQL中出现大小写为空的问题

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

The above query does not returns any result. I think above query has issue with the 'AddlDataFieldCategoryId =' and the null from the case. Can anybody correct the query?

Answer 1

The issue with your CASE expression is that you are comparing a column to a predicate which might be NULL using the equals operator. This won't behave as expected, because NULL comparisons should use IS NULL instead of equals. One possible workaround would be to coalesce AddlDataFieldGroupId to a numeric value. Then, we can be certain that the CASE expression would only be comparing one number to another.

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

Answer 2

If your AddlDataFieldGroupId cannot be zero, then you don't need the CASE at all. This will do the job:

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

If AddlDataFieldGroupId can be zero, but cannot be negative, you can do this:

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

Alternatively, this will work regardless of what AddlDataFieldGroupId can be:

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

Note: all these solutions assume that AddlDataFieldGroupId cannot be NULL .