Question

我需要一个函数，但似乎无法正确使用它，我已经在这里和其他地方查看了示例，似乎无法正确得到这个，我需要一个可选项包含在我的查询中，我有这个查询（有效）：

SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR
(1000),Description)) AS LenDesc FROM tblItem
WHERE Title = @Title AND Manufacturer = @Manufacturer
ORDER BY LenDesc DESC

这在一个函数中有效，但是制造商对于此搜索是可选的 - 这是为了找到类似项目的描述，如果不存在，则另一个查询是：

SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR
(1000),Description)) AS LenDesc FROM tblItem
WHERE Title = @Title ORDER BY LenDesc DESC

哪个缺少制造商，如何让我的功能使用基于制造商价值的查询或不存在。原因是我将有一个函数首先检查SKU的描述，如果它不存在 - 它使用此方法从类似产品获取描述，然后使用类似产品的描述更新正在添加的产品。

这是迄今为止的功能：

ALTER FUNCTION [dbo].[GetDescriptionByTitleManufacturer]
(   
    @Title varchar(400),
    @Manufacturer varchar(160)
)
RETURNS TABLE 
AS
RETURN (
    SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR
    (1000),Description)) AS LenDesc FROM tblItem
    WHERE Title = @Title AND Manufacturer = @Manufacturer
    ORDER BY LenDesc DESC
    )

我尝试过添加BEGIN和IF ... ELSE，但每次尝试都会遇到错误或语法问题，我希望能够做一些像这样的伪函数（这不起作用）：

ALTER FUNCTION [dbo].[GetDescriptionByTitleManufacturer]
(   
    @Title varchar(400),
    @Manufacturer varchar(160)
)
RETURNS TABLE 
AS
BEGIN
IF (@Manufacturer = Null)
RETURN (
    SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR
    (1000),Description)) AS LenDesc FROM tblItem
    WHERE Title = @Title ORDER BY LenDesc DESC
    )
ELSE
RETURN (
    SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR
    (1000),Description)) AS LenDesc FROM tblItem
    WHERE Title = @Title AND Manufacturer = @Manufacturer
    ORDER BY LenDesc DESC
    )

END

Answer 1

你可以这样做吗？

ALTER FUNCTION [dbo].[GetDescriptionByTitleManufacturer]
(   
    @Title varchar(400),
    @Manufacturer varchar(160)
)
RETURNS TABLE 
AS
RETURN (
    SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR
    (1000),Description)) AS LenDesc FROM tblItem
    WHERE Title = @Title AND (@Manufacturer IS NULL OR Manufacturer = @Manufacturer)
    ORDER BY LenDesc DESC
    )

Answer 2

执行AND (Manufacturer = @Manufacturer OR @Manufacturer IS NULL)时，您将无法使用索引。动态搜索有许多微妙的性能影响，您应该阅读Dynamic Search Conditions in T-SQL by Erland Sommarskog

如果您拥有正确的SQL Server 2008版本（SQL 2008 SP1 CU5（10.0.2746）及更高版本），则可以使用此小技巧实际使用索引：

将OPTION (RECOMPILE)添加到您的查询see Erland's article，SQL Server将根据本地值创建查询计划之前从OR内解析(@Manufacturer IS NULL OR Manufacturer = @Manufacturer)变量和索引都可以使用。

ALTER FUNCTION [dbo].[GetDescriptionByTitleManufacturer]
(   
    @Title varchar(400),
    @Manufacturer varchar(160)
)
RETURNS TABLE 
AS
RETURN
(SELECT TOP 100 
     PERCENT SKU, Description, LEN(CONVERT(VARCHAR(1000),Description)) AS LenDesc 
     FROM tblItem
         WHERE Title = @Title 
         AND (@Manufacturer IS NULL OR Manufacturer = @Manufacturer)
     ORDER BY LenDesc DESC
     OPTION (RECOMPILE) ---<<<<only valid for SQL 2008 SP1 CU5 (10.0.2746) and later
)
GO

Answer 3

当制造商不适用时，您可以尝试使用NULL：

SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR
(1000),Description)) AS LenDesc FROM tblItem
WHERE Title = @Title AND (Manufacturer = @Manufacturer OR @Manufacturer IS NULL)
ORDER BY LenDesc DESC

如何获取SQL函数运行不同的查询并从任一查询返回值？

3 个答案: