Question

我正在编写一个返回排序列表的第一个值的SQL函数，但我真的不知道如何启动？该函数只有一个参数，即列表编号（VRI.Listing_Number）

使用select语句，我有：

SELECT  TOP 1 
        --VRI.Listing_RID, VRI.Listing_Number, VRI.Listing_Price, CH.Old_Price, CH.Date_Time_Changed
        CH.Old_Price
FROM    dbo.View_Report_Information_Tables VRI WITH (NOLOCK) 
        INNER JOIN dbo.MLS_Change_History CH WITH (NOLOCK) ON
            VRI.Listing_RID = CH.Listing_RID
        INNER JOIN dbo.MLS_Change_History_Type CHT WITH (NOLOCK) ON
            CH.Transaction_RID = CHT.Transaction_RID
WHERE   CHT.Change_Type_Display = 3 AND
        VRI.Listing_RID = CH.LISTING_RID
ORDER BY CH.Transaction_RID DESC

此sql查询从价格列表中返回最后的价格变化。

我是sql的新手，所以我甚至不太了解语法。例如，我查找了CH.Old_Price，我看到它TYPE_NAME是numeric，但它也有长度和精度，比例......这个函数的返回值应该是多少？？

有什么想法吗？

谢谢，

Answer 1

假设您发布的select语句返回正确的数据，函数的语法相当简单：

CREATE FUNCTION <Inline_Function_Name, sysname, FunctionName> 
(   
-- Add the parameters for the function here
@Listing_Number int, 
)
RETURNS TABLE 
AS
RETURN 
(
-- Add the SELECT statement with parameter references here
)

您也可以通过右键点击SSMS中的Functions来获取此信息 - ＆gt;对象资源管理器 - ＆gt; - ＆GT;可编程性并选择正确的功能类型。我上面的示例假定这返回整行数据（似乎是这种情况）。我还假设VRI.Listing_Number是一个int。

Answer 2

CREATE FUNCTION dbo.FirstPriceChange(@Listing_Number int)
RETURNS MONEY
WITH RETURNS NULL ON NULL INPUT
AS
BEGIN
RETURN (
    SELECT  TOP 1 
            CH.Old_Price
    FROM    dbo.View_Report_Information_Tables VRI WITH (NOLOCK) 
            INNER JOIN dbo.MLS_Change_History CH WITH (NOLOCK) ON
                VRI.Listing_RID = CH.Listing_RID
            INNER JOIN dbo.MLS_Change_History_Type CHT WITH (NOLOCK) ON
                CH.Transaction_RID = CHT.Transaction_RID
    WHERE   CHT.Change_Type_Display = 3 AND
            VRI.Listing_RID = CH.LISTING_RID AND
            VRI.Listing_Number = @Listing_Number
    ORDER BY CH.Transaction_RID DESC
)
END
GO

样本用法：

SELECT
    VRI.Listing_RID, VRI.col1, VRI.Col2,
    dbo.FirstPriceChange(VRI.Listing_Number) AS FirstPriceChange
FROM dbo.View_Report_Information_Tables VRI

注意：

RETURNS MONEY它会返回一种货币类型
WITH RETURNS NULL ON NULL INPUT如果输入为null，则返回null
返回值是单个值，来自子查询，并添加了VRI.Listing_Number过滤器

Answer 3

SELECT TOP 1 FROM (

SELECT *
FROM    dbo.View_Report_Information_Tables VRI WITH (NOLOCK) 
        INNER JOIN dbo.MLS_Change_History CH WITH (NOLOCK) ON
            VRI.Listing_RID = CH.Listing_RID
        INNER JOIN dbo.MLS_Change_History_Type CHT WITH (NOLOCK) ON
            CH.Transaction_RID = CHT.Transaction_RID
WHERE   CHT.Change_Type_Display = 3 AND
        VRI.Listing_RID = CH.LISTING_RID
ORDER BY CH.Transaction_RID DESC

) AS `aaa`

如何创建一个在SQL中返回排序列表的第一个值的函数？

3 个答案: