如何在SQL Server中查找记录中的更改

小编典典

如何在SQL Server中查找记录中的更改

sql

我有一张表，上面有学生信息。

+==========================================+
| ID      |  Department     | Date         |
+==========================================+
| 001     | English         | Feb 3 2017   |
| 001     | English         | Feb 4 2017   |
| 001     | Science         | Mar 1 2017   |
| 001     | Maths           | Mar 2 2017   |
| 001     | Maths           | Mar 21 2017  |
| 001     | Maths           | Apr 2 2017   |
| 001     | English         | Apr 7 2017   |
| 002     | Maths           | Feb 1 2017   |
| 002     | Maths           | Apr 7 2017   |
| 003     | Maths           | Apr 3 2017   |
| 003     | Maths           | Apr 7 2017   |
| 004     | Science         | Feb 1 2017   |
| 004     | Science         | Mar 1 2017   |
| 004     | Maths           | Apr 7 2017   |
| 004     | English         | Apr 9 2017   |
+==========================================+

在上表中，无论何时更改学生的部门偏好，我都需要获取学生记录列表。学生还有机会再次改回同一部门。因此，对于上述示例数据，返回的记录列表为

对于学生001

| 001     | English         | Feb 4 2017   |
| 001     | Science         | Mar 1 2017   |
| 001     | Maths           | Apr 2 2017   |

002和003什么都没有

为004

| 004     | Science         | Mar 1 2017   |
| 004     | Maths           | Apr 7 2017   |

阅读 212

2021-05-16

共1个答案

小编典典

您可以使用LEAD窗口功能-适用于SQL版本2012及更高版本…

DECLARE @SampleData AS TABLE 
(
   Id int,
   Department varchar(20),
   [Date] date
)

INSERT INTO @SampleData
VALUES (1,'English', 'Feb 3 2017'),(1,'English', 'Feb 4 2017'),(1,'Science', 'Mar 1 2017'),
(1,'Maths', 'Mar 2 2017'),(1,'Maths', 'Mar 3 2017'),(1,'English', 'Mar 7 2017'),
(2,'Maths', 'Feb 3 2017'),(2,'Maths', 'Feb 4 2017'),
(3,'Maths', 'Feb 3 2017'), (3,'Maths', 'Feb 4 2017'),
(4,'Science', 'Feb 1 2017'), (4,'Science', 'Feb 2 2017'), (4,'Maths', 'Feb 3 2017'),(4,'English', 'Feb 4 2017')

;WITH temps AS 
(
   SELECT sd.*, LEAD(sd.Department, 1) OVER(PARTITION BY id ORDER BY sd.[Date])  AS NextDepartment
   FROM @SampleData sd    
)
SELECT t.id, t.Department,t.[Date] FROM temps t
WHERE t.Department != t.NextDepartment

演示链接：Rextester

参考链接：LEAD-MDSN

对于较旧的版本，您可以使用 OUTER APPLY

SELECT sd.*
FROM @SampleData sd
OUTER APPLY 
(
   SELECT TOP 1 * FROM @SampleData sd2 WHERE sd.Id = sd2.Id AND sd.[Date] < sd2.[Date]
) nextDepartment
WHERE sd.Department != nextDepartment.Department

2021-05-16