如何对这些数据进行分组，以便我可以从每个组中提取特定行答案

【问题标题】：How to group this data so I can pull out specific rows from each group如何对这些数据进行分组，以便我可以从每个组中提取特定行
【发布时间】：2017-06-27 20:00:11
【问题描述】：

我有如下所示的数据集。由此，我想从PersonIDs 状态已更改为与前一个不同状态的每个组中选择第一行。

例如，从这个数据集中，我想要第 1、4、7 和 11 行。
有什么帮助吗？
如果我执行 GROUPBY，它只会将所有 New 和所有 Pending 归为 2 组。

PersonID    Status  WhenChanged
101         New     27/01/2017 15:27
101         New     27/01/2017 16:40
101         New     27/01/2017 16:40
101         Pending 27/01/2017 16:40
101         Pending 27/01/2017 16:40
101         Pending 27/01/2017 16:40
101         New     31/01/2017 09:14
101         New     31/01/2017 10:02
101         New     31/01/2017 10:03
101         New     31/01/2017 10:05
101         Pending 03/02/2017 14:29
101         Pending 03/02/2017 14:29

【问题讨论】：

标签： sql sql-server-2008 group-by

【解决方案1】：

试一试...使用 CTE。订购已关闭，因为您使用的日期是 varchar 格式或显示为 varchar 格式。您可以将其转换为相同的，这将正常工作。

declare @table table (PersonID int, Status varchar(16), WhenChanged varchar(64))
insert into @table values
(101,'New','27/01/2017 15:27'),
(101,'New','27/01/2017 16:40'),
(101,'New','27/01/2017 16:40'),
(101,'Pending','27/01/2017 16:40'),
(101,'Pending','27/01/2017 16:40'),
(101,'Pending','27/01/2017 16:40'),
(101,'New','31/01/2017 09:14'),
(101,'New','31/01/2017 10:02'),
(101,'New','31/01/2017 10:03'),
(101,'New','31/01/2017 10:05'),
(101,'Pending','03/02/2017 14:29'),
(101,'Pending','03/02/2017 14:29')

;with cte as(
    select
        PersonID,
        Status,
        WhenChanged,
        case when lag(Status) over (partition by PersonID order by convert(datetime,WhenChanged,103)) <> Status then 1 else 0 end as d
    from
        @table)



select top 1 *
from @table
union 
select  PersonID,
        Status,
        WhenChanged
from cte
where d=1
order by WhenChanged

SQL Server 2008 及以前的版本

declare @table table (PersonID int, Status varchar(16), WhenChanged varchar(64))
insert into @table values
(101,'New','27/01/2017 15:27'),
(101,'New','27/01/2017 16:40'),
(101,'New','27/01/2017 16:40'),
(101,'Pending','27/01/2017 16:40'),
(101,'Pending','27/01/2017 16:40'),
(101,'Pending','27/01/2017 16:40'),
(101,'New','31/01/2017 09:14'),
(101,'New','31/01/2017 10:02'),
(101,'New','31/01/2017 10:03'),
(101,'New','31/01/2017 10:05'),
(101,'Pending','03/02/2017 14:29'),
(101,'Pending','03/02/2017 14:29')


;with cte as(
    select 
        PersonID,
        Status,
        convert(datetime,WhenChanged,103) as WhenChanged,
        row_number() over (order by personID, convert(datetime,WhenChanged,103)) as RN
    from
        @table),

cteResults as(
    select
        PersonID,
        Status,
        WhenChanged
    from
        cte 
    where RN = 1
    UNION
    select
        c.PersonID,
        c.Status,
        c.WhenChanged 
    from
        cte c
    inner join
        cte c2 on c2.rn = (c.rn -1) and c2.status <> c.status)

select * from cteResults order by WhenChanged

【讨论】：

非常感谢。不幸的是，当我尝试运行它时，我意识到我只有 sql server 2008，并且 lag 功能不起作用。有没有其他方法可以不延迟地写这个？
@Tan 我对 2016 年之前的帖子进行了编辑。请注意，您标记了 SQL Server 2016，这就是我使用 LAG() 的原因。确保下次标记正确的版本。我已更改您的问题以反映正确的标签。