Question

我需要创建一个SQL Server 2012 SELECT语句，它将为我提供表格中的上一行。我需要指定当前的日期时间，并让查询返回[TargetDate]列中存储的最接近的上一个日期时间。

所以在表格中我可能有......

[TargetUnit]    [TargetDate]
-----------------------------------
4               2015-12-09 10:15:00 
5               2015-12-09 10:30:00
8               2015-12-09 10:45:00
15              2015-12-09 11:00:00
22              2015-12-09 11:15:00

我使用GETDATE()来查询[TargetDate]字段。说当前GETDATE()是2015-12-09 10:37:00 - 然后我需要查询返回[TargetUnit] 5和[TargetDate] 2015-12-09 10:30:00的行

Answer 1

您可以使用top和order by来获取所需的记录。

select top 1 [TargetUnit], [TargetDate]
  from tbl
 where [TargetDate] < GETDATE()
 order by [TargetDate] desc

Answer 2

可以使用datediff和while循环来做，我应该说这是我能想到的最佳选择，如果你正在处理一个可能有FUTURE日期时间的表。直到找到指定日期的最接近的值，未来或过去。

DECLARE @targetdate datetime
DECLARE @getdate datetime = GETDATE()
DECLARE @targetunit int

CREATE TABLE #diffs (targetunit int, targetdate datetime, diffday, diffsec int)

SELECT * INTO #table FROM YOUR_TABLE
WHILE (SELECT COUNT(*) FROM #TABLE) > 0
BEGIN
SELECT TOP 1 @targetunit = targetunit, @targetdate = targetdate FROM #table
DELETE FROM #table WHERE targetunit = @targetunit and targetdate = @targetdate

INSERT INTO #diff
SELECT @targetunit, @targetdate, datediff(day, @targetdate, @getdate),         Datediff(second, @targetdate, @getdate)
END

SELECT targetunit, targetdate, MIN(diffday) diffday, MIN(diffsec) diffsec
INTO #mins
FROM #diff 

SELECT *
FROM #diff a
JOIN #mins b on a.targetunit = b.targetunit
WHERE a.diffday = b.diffday and a.diffsec = b.diffsec

需要SQL Server SELECT基于DateTime返回上一个记录

2 个答案: