选择Top 1字段并分配给本地变量

Question

我想从此查询中获取ExtractedDate的值,并在下一个查询中将其用作@LastExtractDate.我怎么做？

    SELECT TOP 1 [ExtractedDate]
    FROM [OnsiteV4].[dbo].[SqlPendingIndex] order by ExtractedDate desc

下一个查询:

    insert into @table(Hex, KeyDeviceId, ObjectDateTime, ExtractedDate  )
SELECT     CONVERT(VARCHAR(MAX), CONVERT(VARBINARY(MAX), ObjectValue, 1)) AS Hex, KeyDeviceId, ObjectDateTime , GETDATE ()
    FROM         SQLPending
    WHERE     (ObjectSubType LIKE '%GAS%') and (ObjectDateTime > @LastExtractDate)

Answer 1

为什么不用这个:

declare @LastExtractDate date
SELECT TOP 1 @LastExtractDate=[ExtractedDate]
FROM [OnsiteV4].[dbo].[SqlPendingIndex] order by ExtractedDate desc

Answer 2

用这个：

DECLARE @ExtractedDate DATETIME
SET  @ExtractedDate = (SELECT    TOP 1 ExtractedDate
                       FROM      [OnsiteV4].[dbo].[SqlPendingIndex]
                       ORDER BY  ExtractedDate DESC

Answer 3

只需声明并指定:

DECLARE @LastExtractDate DATETIME = (
    SELECT TOP 1 [ExtractedDate] FROM [OnsiteV4].[dbo].[SqlPendingIndex] order by ExtractedDate desc
)

或更好:

DECLARE @LastExtractDate DATETIME = (
    SELECT MAX(ExtractedDate) FROM [OnsiteV4].[dbo].[SqlPendingIndex]
)

Answer 4

简单地试试这个

declare @LastExtractDate date 
SELECT @LastExtractDate=MAX([ExtractedDate])
FROM [OnsiteV4].[dbo].[SqlPendingIndex]