如何对这些数据进行分组，以便从每个组中抽出特定行

Question

我拥有下面显示的数据集。因此，我想从每个组中选择第一行，其中PersonID的状态已更改为与先前状态不同的状态。

例如，从这个数据集，我想第1,4,7和11行。
对此有什么帮助？
如果我做了一个GROUPBY，它只是将所有新建和所有挂起组合在一起。

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 

Answer 1

这是一个去...使用CTE。由于您使用的日期是以varchar格式显示或因此显示，所以排序不起作用。你可以将它转换成相同的，这将工作正常。

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和以前版本

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