Calculate date difference between dates in different rows of a dataset - sql

Question

A table looks like this :
CREATE TABLE [dbo].[HistDT](
[ID] [bigint] NULL,
[StartDtSK] [varchar](8) NULL,
[StartDt] [datetime] NULL,
[status] [nvarchar](30) NULL,
) ON [PRIMARY]
Example data set:
ID | StartDtSK | StartDt | Status |
1 20190520 20-05-2019 12:00:13 10
1 20190520 20-05-2019 10:00:00 5
1 20190414 14-04-2019 13:23:00 2
2 20190312 12-03-2019 10:03:00 10
2 20190308 08-03-2019 18:03:00 1
etc..
I need a query which will display the number of days spent in each status. That would be easy if the table i inherited had an end date. I would then calculate the datediff and pivot for column status values.
Maybe i should create a new table using ssis where i will add an EndDt column which will be the StartDt of the latest added Status.
But is there any way to do this without creating another table?

Answer 1

SQL Server 2008
This is not very pretty, and I haven't tested it for all use cases. I hope you can use it or find inspiration. I'm sure there is a better way :)
declare #table2 table (
[ID] [bigint] NULL,
[StartDtSK] [varchar](8) NULL,
[StartDt] [datetime] NULL,
[status] [nvarchar](30) NULL
)
insert into #table2
values
(1 , '20190520','2019-05-20 12:00:13','10'),
(1 , '20190520','2019-05-20 10:00:00','5'),
(1 , '20190414','2019-04-14 13:23:00','2'),
(2, '20190312', '2019-03-12 10:03:00', '10'),
(2 , '20190308', '2019-03-08 18:03:00', '1')
select *,DATEDIFF(dd,startdt,enddate) as TotalDAys from (
select x.ID,StartDtSK,Startdt,[Status],Enddate from (
select *,ROW_NUMBER() over(partition by id order by startdt) as rn from #table2
) x
cross apply ( select * from (select id,StartDt as Enddate,ROW_NUMBER() over(partition by id order by startdt) as rn2 from #table2 b
)f where (rn +1 = f.rn2 ) and x.id = f.id ) d
union all
select ID,StartDtSK,startdt,[Status],'9999-12-31' as Enddate from (
select *,ROW_NUMBER() over(partition by id order by startdt desc) as rn from #table2
)X where rn=1
)y
order by id,startdt
SQL Server 2008 without cross apply
This might be a bit more pretty :)
select *,DATEDIFF(dd,startdt,enddate) as TotalDAys from (
select x.ID,StartDtSK,Startdt,[Status],case when Enddate is null then '9999-12-31' else Enddate end as Enddate from (
select *,ROW_NUMBER() over(partition by id order by startdt) as rn from #table2
) x
left join (
select * from (select id,StartDt as Enddate,ROW_NUMBER() over(partition by id order by startdt) as rn2 from #table2 b
)f ) d on (rn +1 = d.rn2 ) and x.id = d.id
)y
SQL Server 2012 and above:
Is this what you want?
declare #table2 table (
[ID] [bigint] NULL,
[StartDtSK] [varchar](8) NULL,
[StartDt] [datetime] NULL,
[status] [nvarchar](30) NULL
)
insert into #table2
values
(1 , '20190520','2019-05-20 12:00:13','10'),
(1 , '20190520','2019-05-20 10:00:00','5'),
(1 , '20190414','2019-04-14 13:23:00','2')
select *,Datediff(dd,Startdt,Enddate) as TotalDays from (
select *,LAG(StartDt,1,'9999-12-31') over(partition by ID order by StartDT desc) as EndDate from #table2
)x
Insert a rule that handles current status (9999-12-31) date

Answer 2

Maybe LEAD function is usefull for your question.
Like this
IsNull(DateAdd(SECOND,-1,Cast(LEAD ([StartDt],1) OVER (PARTITION BY [status] ORDER BY [StartDt]) AS DATETIME)),getdate()) AS EndDate