Select 随着时间的推移，每个不同的值都不会丢失其间的 NULL

Question

让我们假设一个 table 有很多列，一个 Temporal table 正在记录它的历史。有一个字段我需要知道它何时更改。

Number	VersionStartDate
991281	2021-11-12 08:27:11
991281	2021-11-12 08:20:11
NULL	2021-11-12 07:20:11
NULL	2021-11-12 06:20:11
771281	2021-11-11 08:26:11
NULL	2021-11-11 08:25:11
661281	2021-11-10 08:24:11
NULL	2021-11-10 08:22:11
661281	2021-11-10 08:21:11
551281	2021-11-09 08:20:11

我需要获取每个值，以及它发生变化的时刻。我还需要知道它是否已设置为 NULL，因此此查询未提供我需要的信息。

SELECT
    Number,
    MIN(VersionStartDate) [Date]
FROM _TABLE_ 
GROUP BY
    Number
ORDER BY
    [Date] DESC

结果应该是

Number	VersionStartDate
991281	2021-11-12 08:20:11
NULL	2021-11-12 06:20:11
771281	2021-11-11 08:26:11
NULL	2021-11-11 06:25:11
661281	2021-11-10 08:24:11
NULL	2021-11-10 08:22:11
661281	2021-11-10 08:21:11
551281	2021-11-09 08:20:11

Answer 1

在您的组中添加 VersionStartDate。

SELECT
    Number,
    MIN(VersionStartDate)
FROM _TABLE_ 
GROUP BY
    Number, VersionStartDate
ORDER BY
    VersionStartDate DESC

Answer 2

好吧，这是一种方法，我相信还有更多 eloquent 的方法来编写它，但它可以帮助您入门：

CREATE TABLE #T(Number int, VersionStartDate datetime)
INSERT INTO #T vALUES
(991281,'2021-11-12 08:27:11'),
(991281,'2021-11-12 08:20:11'),
(NULL,'2021-11-12 07:20:11'),
(NULL,'2021-11-12 06:20:11'),
(771281,'2021-11-11 08:26:11'),
(NULL,'2021-11-11 08:25:11'),
(661281,'2021-11-10 08:24:11'),
(NULL,'2021-11-10 08:22:11'),
(661281,'2021-11-10 08:21:11'),
(551281,'2021-11-09 08:20:11')


SELECT Number, MIN(VersionStartDate) VersionStartDate
FROM
(
    SELECT *, SUM(CASE WHEN ISNULL(Number,-1) <> ISNULL(LG,-1) THEN 1 ELSE 0 END) OVER(ORDER BY VersionStartDate desc) GRP
    FROM
    (
        SELECT *, LAG(Number,1,-1) OVER(ORDER BY VersionStartDate desc) LG
        FROM #T
    ) X
) Y
GROUP BY GRP,Number
ORDER BY VersionStartDate desc

Answer 3

和我开始研究后出现的JMabee很相似，但可能更简单一点：

CREATE TABLE #d (Number INT, VersionStartDate DATETIME);
INSERT INTO #d(Number, VersionStartDate) 
VALUES
(991281 ,'2021-11-12T08:27:11'),
(991281 ,'2021-11-12T08:20:11'),
(NULL   ,'2021-11-12T07:20:11'),
(NULL   ,'2021-11-12T06:20:11'),
(771281 ,'2021-11-11T08:26:11'),
(NULL   ,'2021-11-11T08:25:11'),
(661281 ,'2021-11-10T08:24:11'),
(NULL   ,'2021-11-10T08:22:11'),
(661281 ,'2021-11-10T08:21:11'),
(551281 ,'2021-11-09T08:20:11');

WITH cte AS
(
    SELECT  Number,
            VersionStartDate,
            LAG(Number, 1) OVER (ORDER BY VersionStartDate) AS PrevNumber
    FROM    #d
)
SELECT      cte.Number,
            cte.VersionStartDate
FROM        cte
WHERE       ISNULL(cte.Number, -1) <> ISNULL(cte.PrevNumber, -1)
ORDER BY    cte.VersionStartDate DESC;

Select 随着时间的推移，每个不同的值都不会丢失其间的 NULL

Select each distinct value over time without losing NULLs in between

sql

tsql

sql-server

gaps-and-islands