如何在 SQL Server 2008 中的 Case 语句中返回 Null

Question

我想返回空值以防万一。这是我的查询

Declare @MasterProduct nvarchar(50) = N'Sharepoint Easy Nav',
        @ProductSlug nvarchar(50) = 'sharepoint-easynav-free',
        @CountryID bigint = 1111;

SELECT        
Product.ProductName, 
Product.MasterProductName, 
Price.ProductPrice, 
Price.ProductTax, 
Price.ProductTotalPrice, 
Product.TotalSiteCollectionText, 
Product.TotalSiteCollection, 
Product.Is_Support, 
Price.Is_Support_Price, 
Product.ProductSlug, 
Country.CountrySymbol, 
Country.CountryId
FROM
BR_Product as Product 
Inner Join BR_ProductPrice as Price on Product.ID = Price.ProductID 
left Join BR_Country as Country On Price.CountryID = Country.CountryId 
where Product.MasterProductName = IsNull(@MasterProduct, Product.MasterProductName) 
and Product.ProductSlug = IsNull(@ProductSlug, Product.ProductSlug) 
and Country.CountryId = case 
                          when (select count(BR_ProductPrice.ID) 
                                from BR_ProductPrice 
                                where  BR_ProductPrice.CountryID = @CountryID) > 0 
                          Then @CountryID 
                          else Null
                        end

它没有返回任何行。
当我删除

Country.CountryId = case when (select count(BR_ProductPrice.ID) from BR_ProductPrice where BR_ProductPrice.CountryID = @CountryID) > 0 Then @CountryID else Null 结束

它返回我以下内容：

我希望 CountryId 比较 else 部分中 case 语句的 null 部分，类似这样

然后@CountryID 否则 Country.CountryId 为空

当我通过 CountryID = 1101 时，查询工作正常。

Answer 1

在 where 条件和条件上使用 ISNULL(CountryID,'') 并将 = null 替换为 = ''

Inner Join BR_ProductPrice as Price on Product.ID = Price.ProductID 
left Join BR_Country as Country On isnull(Price.CountryID,'') = isnull(Country.CountryId,'') 
where Product.MasterProductName = ISNULL(@MasterProduct, Product.MasterProductName) 
and Product.ProductSlug = ISNULL(@ProductSlug, Product.ProductSlug) 
and ISNULL(Country.CountryId,'') = case 
                      when (select count(BR_ProductPrice.ID) 
                            from BR_ProductPrice 
                            where  ISNULL(BR_ProductPrice.CountryID,'') = @CountryID) > 0 
                      Then @CountryID 
                      else ''
                    end

Answer 2

尝试改变这一点

来自：

Country.CountryId = case 
                          when (select count(BR_ProductPrice.ID) 
                                from BR_ProductPrice 
                                where  BR_ProductPrice.CountryID = @CountryID) > 0 
                          Then @CountryID 
                          else Null
                        end

收件人：

Country.CountryId =(select Case when cnt_BR_ProductPriceID > 0 then @CountryID else null end from
(select count(BR_ProductPrice.ID) as cnt_BR_ProductPriceID from BR_ProductPrice where  BR_ProductPrice.CountryID = @CountryID) as cnt)

从未尝试过。

希望它有效。

Answer 3

您不能将= 与null 一起使用。试试这个：

and (
    (Country.CountryId = @CountryID 
     and (select count(BR_ProductPrice.ID) 
          from BR_ProductPrice 
          where  BR_ProductPrice.CountryID = @CountryID) > 0 
    ) 
    OR Country.CountryId IS NULL
    )