压缩历史表的SQL server组/分区

Question

得到一个日期表，某人属于这样的特定类别:

drop table if exists #category
create table #category (personid int, categoryid int, startdate datetime, enddate datetime)
insert into #category 
select * from 
(
select 1 Personid, 1 CategoryID, '01/04/2010' StartDate, '31/07/2016' EndDate union
select 1 Personid, 5 CategoryID, '07/08/2016' StartDate, '31/03/2019' EndDate union
select 1 Personid, 5 CategoryID, '01/04/2019' StartDate, '01/04/2019' EndDate union
select 1 Personid, 5 CategoryID, '02/04/2019' StartDate, '11/08/2019' EndDate union
select 1 Personid, 4 CategoryID, '12/08/2019' StartDate, '03/11/2019' EndDate union
select 1 Personid, 5 CategoryID, '04/11/2019' StartDate, '22/03/2020' EndDate union
select 1 Personid, 5 CategoryID, '23/03/2020' StartDate, NULL EndDate union
select 2 Personid, 1 CategoryID, '01/04/2010' StartDate, '09/04/2015' EndDate union
select 2 Personid, 4 CategoryID, '10/04/2015' StartDate, '31/03/2018' EndDate union
select 2 Personid, 4 CategoryID, '01/04/2018' StartDate, '31/03/2019' EndDate union
select 2 Personid, 4 CategoryID, '01/04/2019' StartDate, '23/06/2019' EndDate union
select 2 Personid, 4 CategoryID, '24/06/2019' StartDate, NULL EndDate 
) x
order by personid, startdate

我试着压缩它，所以我得到这个:

tbody> <<tr>11122

PersonID	categoryid	起始日期	结束日期
1	1	01/04/2010	31/07/2016
	5	07/08/2016	11/08/2019
	4	12/08/2019	03/11/2019
	5	04/11/2019	空
	1	01/04/2010	09/04/2015
	4	01/04/2015	空

这是一种缺口和孤岛问题。但是，如果您的数据完全平铺(没有间隙)，就像您的示例数据一样，那么您就可以完全不进行任何聚合—这应该是最有效的方法:

select personid, categoryid, startdate,
dateadd(day, -1, lead(startdate) over (partition by personid order by startdate)) as enddate
from (select c.*,
lag(categoryid) over (partition by personid order by startdate) as prev_categoryid
from #category c
) c
where prev_categoryid is null or prev_categoryid <> categoryid;

where子句只选择类别发生变化的行。然后lead()获得下一个开始日期，并为您想要的enddate减去1。