我有一个表,其中包含链接到另一个表的优先级记录。
FK - Priority - PriorityUpdateDateTime
我要做的是在此表中添加结束日期,但仅作为临时表。
所以我需要的是FK - Priority - StartDate - EndDate
其中EndDate是下一个PriorityUpdateDateTime
即
FK - Priority - PriorityUpdateDateTime
123 - 4 - 2011-02-25
123 - 2 - 2011-02-30
123 - 3 - 2011-03-10
变为
FK - Priority - StartDate - EndDate
123 - 4 - 2011-02-25 - 2011-02-30
123 - 2 - 2011-02-30 - 2011-03-10
123 - 3 - 2011-03-10 - NULL
感谢您的帮助
答案 0 :(得分:1)
好的,你可以使用这样的子选择:
-- nasty sub select, lets see if we can do better
SELECT T1.[FK],
T1.[Priority],
T1.[PriorityUpdateDateTime] AS 'StartDate',
(
SELECT MAX(T2.[PriorityUpdateDateTime]) AS MP
FROM @test AS T2
WHERE T2.[FK] = T1.[FK]
AND T2.[Priority] < T1.[Priority]
) AS 'EndDate'
FROM @test AS T1
这是我创建测试表和数据的临时脚本
DECLARE @test AS TABLE
(
[FK] INT NOT NULL,
[Priority] INT NOT NULL,
[PriorityUpdateDateTime] DATETIME NOT NULL
)
INSERT INTO @test VALUES(123, 4, '20110225')
INSERT INTO @test VALUES(123, 3, '20110228') -- there are only 28 days in Feb in 2011 (not 30)
INSERT INTO @test VALUES(123, 2, '20110310')
-- nasty sub select, lets see if we can do better
SELECT T1.[FK],
T1.[Priority],
T1.[PriorityUpdateDateTime] AS 'StartDate',
(
SELECT MAX(T2.[PriorityUpdateDateTime]) AS MP
FROM @test AS T2
WHERE T2.[FK] = T1.[FK]
AND T2.[Priority] < T1.[Priority]
)
FROM @test AS T1
答案 1 :(得分:0)
@Matt @Kane
凯恩做得很好,除了他为不平等选择了错误的专栏。我刚做了一些修正。如果有人能够提出一种更快速的方法,而不是“古怪的更新”,这将会打破相关的子查询和CROSS APPLY方法,我会感到惊讶。这是构建更多测试数据的代码,而不是为了进行性能测试而动摇。
--===== Conditionallly drop the test table to make reruns in SSMS easier
IF OBJECT_ID('tempdb..#Test','U') IS NOT NULL
DROP TABLE #Test
;
--===== Create and populate the test table on-the-fly
-- using a "Pseudo Cursor" which is many times
-- faster than a WHILE loop.
SELECT TOP 100000
FK = ABS(CHECKSUM(NEWID()))%100+100, -- 100 thru 199
Priority = ABS(CHECKSUM(NEWID()))%100+1, -- 1 thru 100
PriorityUpdateDateTime = DATEADD(dd,
ABS(CHECKSUM(NEWID()))%DATEDIFF(dd,'2000','2010')
,'2000') --20000101 thru 20091231
INTO #Test
FROM sys.all_columns ac1 --has more than 4000 rows even on a new system
CROSS JOIN sys.all_columns ac2
;
--===== Create a clustered index to improve performance by about 10 times in this case
CREATE INDEX IX_#Test ON #Test (FK,PriorityUpdateDateTime)
;
以下是Kane代码的两个不同版本。详细信息在代码中。两者在大约相同的时间内返回相同的结果。
--===== Kane's correlated subquery works just fine here once we
-- flip it around and use a different column name in the
-- inequality part.
SELECT t1.FK,
t1.Priority,
StartDate = t1.PriorityUpdateDateTime,
EndDate =
(
SELECT MIN(t2.PriorityUpdateDateTime)
FROM #Test t2
WHERE t2.FK = t1.FK
AND t2.PriorityUpdateDateTime > t1.PriorityUpdateDateTime
)
FROM #Test t1
ORDER BY t1.FK, t1.PriorityUpdateDateTime, t1.Priority
;
--===== Or, you could use a CROSS APPLY and get the same thing because
-- a CROSS APPLY isn't much more than a correlated sub-query.
SELECT t1.FK,
t1.Priority,
StartDate = t1.PriorityUpdateDateTime,
d.EndDate
FROM #Test t1
CROSS APPLY
(
SELECT MIN(t2.PriorityUpdateDateTime)
FROM #Test t2
WHERE t2.FK = t1.FK
AND t2.PriorityUpdateDateTime > t1.PriorityUpdateDateTime
) d (EndDate)
ORDER BY t1.FK, t1.PriorityUpdateDateTime, t1.Priority
;