当列值更改时，如何将组号添加到 SQL Server 2012 中的顺序记录？

Question

我一直在使用 SQL Server 2012 中的 window 函数，但无法正常工作，因为我希望避免光标并逐行进行。我的问题是我需要为每条记录添加一个组号。棘手的部分是，每次列值更改时，组号都必须递增，即使它变回记录序列中之前存在的值也是如此。

这是数据示例和我想要的结果：

if object_id('tempdb..#data') is not null 
    drop table #data

create table #data
(
    id int identity(1,1)
    ,mytime datetime
    ,distance int
    ,direction varchar(20)
)

insert into #data (mytime, distance, direction) 
values 
 ('2016-01-01 08:00',10,'North')
,('2016-01-01 08:30',18,'North')
,('2016-01-01 09:00',15,'North')
,('2016-01-01 09:30',12,'South')
,('2016-01-01 10:00',16,'South')
,('2016-01-01 10:30',45,'North')
,('2016-01-01 11:00',23,'North')
,('2016-01-01 11:30',14,'South')
,('2016-01-01 12:00',40,'South')

期望的结果：

mytime              Distance    Direction   GroupNumber
--------------------------------------------------------
2016-01-01 8:00     10          North       1
2016-01-01 8:30     18          North       1
2016-01-01 9:00     15          North       1
2016-01-01 9:30     12          South       2
2016-01-01 10:00    16          South       2
2016-01-01 10:30    45          North       3
2016-01-01 11:00    23          North       3
2016-01-01 11:30    14          South       4
2016-01-01 12:00    40          South       4

这可以使用 window 函数吗？

Answer 1

一种方法是

WITH T
     AS (SELECT *,
                CASE
                  WHEN LAG(direction)
                         OVER (ORDER BY ID) = direction THEN 0
                  ELSE 1
                END AS Flag
         FROM   #data)
SELECT mytime,
       Distance,
       Direction,
       SUM(Flag) OVER (ORDER BY id) AS GroupNumber
FROM   T

以上假定 Direction 不包含任何 NULLs。如果可能的话，它需要一个小的调整。但是您还需要定义两个连续的 NULL 是否应该被视为相等（假设是这种情况，那么下面的变体将起作用）

WITH T
     AS (SELECT *,
                prev = LAG(direction) OVER (ORDER BY ID),
                rn = ROW_NUMBER() OVER (ORDER BY ID)
         FROM   #data)
SELECT mytime,
       Distance,
       Direction,
       SUM(CASE WHEN rn > 1 AND EXISTS(SELECT prev 
                                       INTERSECT 
                                       SELECT Direction) THEN 0 ELSE 1 END) OVER (ORDER BY id) AS GroupNumber
FROM   T 
ORDER BY ID

当列值更改时，如何将组号添加到 SQL Server 2012 中的顺序记录？

How can I add group numbers to sequential records in SQL Server 2012 when a column value changes?

sql

sql-server

window-functions

sql-server-2012