SQL查询根据列值变化查找最早日期

Question

我有一个问题，我需要从按列分组但按顺序分组的表中获取最早的日期值。

这是一个示例表：

if object_id('tempdb..#tmp') is NOT null 
    DROP TABLE #tmp

CREATE TABLE #tmp
(
    UserID              BIGINT      NOT NULL,
    JobCodeID           BIGINT      NOT NULL,
    LastEffectiveDate   DATETIME    NOT NULL
)

INSERT INTO #tmp VALUES ( 1, 5, '1/1/2010') 
INSERT INTO #tmp VALUES ( 1, 5, '1/2/2010') 
INSERT INTO #tmp VALUES ( 1, 6, '1/3/2010') 
INSERT INTO #tmp VALUES ( 1, 5, '1/4/2010') 
INSERT INTO #tmp VALUES ( 1, 1, '1/5/2010') 
INSERT INTO #tmp VALUES ( 1, 1, '1/6/2010')

SELECT JobCodeID, MIN(LastEffectiveDate)
FROM #tmp
WHERE UserID = 1
GROUP BY JobCodeID

DROP TABLE [#tmp]

此查询将返回 3 行，其中包含最小值。

1   2010-01-05 00:00:00.000
5   2010-01-01 00:00:00.000
6   2010-01-03 00:00:00.000

我正在寻找的是该组是连续的并返回多个 JobCodeID，如下所示：

5   2010-01-01 00:00:00.000
6   2010-01-03 00:00:00.000
5   2010-01-04 00:00:00.000
1   2010-01-05 00:00:00.000

没有光标可以吗？

Answer 1

SELECT  JobCodeId, MIN(LastEffectiveDate) AS mindate
FROM    (
        SELECT  *,
                prn - rn AS diff
        FROM    (
                SELECT  *,
                        ROW_NUMBER() OVER (PARTITION BY JobCodeID 
                                    ORDER BY LastEffectiveDate) AS prn,
                        ROW_NUMBER() OVER (ORDER BY LastEffectiveDate) AS rn
                FROM    @tmp
                ) q
        ) q2
GROUP BY
        JobCodeId, diff
ORDER BY
        mindate

连续范围在分区和未分区ROW_NUMBERs之间具有相同的区别。

您可以在GROUP BY 中使用此值。

有关其工作原理的更多详细信息，请参阅我的博客中的这篇文章：

• Grouping continuous ranges

Answer 2

第一条评论 - 使用表变量而不是临时表会更好。然后你可以使用这样的技巧。确保以正确的顺序插入值（即 LastEffectiveDate 升序）：

DECLARE @tmp table
(
    Sequence            INT IDENTITY,
    UserID              BIGINT,
    JobCodeID           BIGINT,
    LastEffectiveDate   DATETIME
)

INSERT INTO @tmp VALUES ( 1, 5, '1/1/2010') 
INSERT INTO @tmp VALUES ( 1, 5, '1/2/2010') 
INSERT INTO @tmp VALUES ( 1, 6, '1/3/2010') 
INSERT INTO @tmp VALUES ( 1, 5, '1/4/2010') 
INSERT INTO @tmp VALUES ( 1, 1, '1/5/2010') 
INSERT INTO @tmp VALUES ( 1, 1, '1/6/2010')

SELECT TOP 1 JobCodeID, LastEffectiveDate
FROM @tmp

UNION ALL

SELECT t2.JobCodeID, t2.LastEffectiveDate
FROM @tmp t1
    INNER JOIN
        @tmp t2
        ON t1.Sequence + 1 = t2.Sequence
WHERE t1.JobCodeID <> t2.JobCodeID

每次工作代码更改时都会输出第一个日期，我猜这就是你想要的描述。