1

我需要一个函数，但似乎无法完全正确，我已经查看了此处和其他地方的示例，但似乎无法正确理解，我需要在我的查询中包含一个可选项目，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

这在函数中有效，但是制造商对于此搜索是可选的 - 这是查找类似项目的描述，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，如何让我的函数根据是否存在制造商值使用任一查询。原因是我将有一个功能，它首先检查 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。

这是到目前为止的功能：

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
    )

我尝试添加 BEGIN 和 IF...ELSE 但每次尝试都会出现错误或语法问题，我希望能够执行类似这个伪函数的操作（它不起作用）：

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
    )

结尾

4

3 回答 3

4

你能做这样的事情吗？

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
    )
于 2010-04-01T10:08:48.037 回答
1

当你这样做时，你就AND (Manufacturer = @Manufacturer OR @Manufacturer IS NULL)消除了索引的使用。动态搜索有许多微妙的性能影响，您应该阅读Erland Sommarskog 的 T-SQL 中的动态搜索条件

如果您有正确的 SQL Server 2008 版本（SQL 2008 SP1 CU5 (10.0.2746) 及更高版本），您可以使用这个小技巧来实际使用索引：

添加OPTION (RECOMPILE)到您的查询中， 请参阅 Erland 的文章，SQL Server 将在根据局部变量的值创建查询计划之前OR从内部解析，并且可以使用索引。(@Manufacturer IS NULL OR Manufacturer = @Manufacturer)

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
于 2010-04-01T11:31:07.317 回答
0

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
于 2010-04-01T10:10:52.183 回答