Overlapping between first record enddate and next record start date in SQL Server - sql

Question

I have the below kind of data and I need below kind of output.
Input:
id startdate enddate
1 21/01/2019 23/01/2019
1 23/01/2019 24/01/2019
1 24/01/2029 27/01/2019
1 29/01/2019 02/02/2019
Output:
id startdate enddate
1 21/01/2019 27/01/2019
1 29/01/2019 02/02/2019
We need to use the logic of matching the first record enddate and nth record startdate.

Answer 1

This is a gaps-and-islands problem, where you want to group together "adjacent" dates. Here is one approach using window functions: the idea is to compare the current start date to the end date of the "previous" row, and use a window sum to define the groups:
select id, min(startdate) startdate, max(enddate) enddate
from (
select t.*,
sum(case when startdate = lag_enddate then 0 else 1 end) over(partition by id order by startdate) grp
from (
select t.*,
lag(enddate) over(partition by id order by startdate) lag_enddate
from mytable t
) t
) t
group by id, grp
Demo on DB Fiddle - with credits to Sander for creating the DDL statements in the first place:
id | startdate | enddate
-: | :--------- | :---------
1 | 2019-01-21 | 2019-01-27
1 | 2019-01-29 | 2019-02-02

Answer 2

have a look at
NEXT VALUE FOR method, works 2016 and later
Use a CTE or subquery (works in 2008) where you join on your own table using the previous value as a join. Here a sample script I use showing backup growth
declare #backupType char(1)
, #DatabaseName sysname
set #DatabaseName = db_name() --> Name of current database, null for all databaseson server
set #backupType ='D' /* valid options are:
D = Database
I = Database Differential
L = Log
F = File or Filegroup
G = File Differential
P = Partial
Q = Partial Differential
*/
select backup_start_date
, backup_finish_date
, DurationSec
, database_name,backup_size
, PreviouseBackupSize
, backup_size-PreviouseBackupSize as growth
,KbSec= format(KbSec,'N2')
FROM (
select backup_start_date
, backup_finish_date
, datediff(second,backup_start_date,b.backup_finish_date) as DurationSec
, b.database_name
, b.backup_size/1024./1024. as backup_size
,case when datediff(second,backup_start_date,b.backup_finish_date) >0
then ( b.backup_size/1024.)/datediff(second,backup_start_date,b.backup_finish_date)
else 0 end as KbSec
-- , b.compressed_backup_size
, (
select top (1) p.backup_size/1024./1024.
from msdb.dbo.backupset p
where p.database_name = b.database_name
and p.database_backup_lsn< b.database_backup_lsn
and type=#backupType
order by p.database_backup_lsn desc
) as PreviouseBackupSize
from msdb.dbo.backupset as b
where #DatabaseName IS NULL OR database_name =#DatabaseName
and type=#backupType
)as A
order by backup_start_date desc
using a "cursor local fast_forward" to loop over the data on a row-by-row and use a temporary table where you store & compaire prev value

Answer 3

Here is a solution with common table expressions that could work.
Sample data
create table data
(
id int,
startdate date,
enddate date
);
insert into data (id, startdate, enddate) values
(1, '2019-01-21', '2019-01-23'),
(1, '2019-01-23', '2019-01-24'),
(1, '2019-01-24', '2019-01-27'),
(1, '2019-01-29', '2019-02-02');
Solution
-- determine start dates
with cte_start as
(
select s.id,
s.startdate
from data s
where not exists ( select 'x'
from data e
where e.id = s.id
and e.enddate = s.startdate )
),
-- determine date boundaries
cte_startnext as
(
select s.id,
s.startdate,
lead(s.startdate) over (partition by s.id order by s.startdate) as startdate_next
from cte_start s
)
-- determine periods
select sn.id,
sn.startdate,
e.enddate
from cte_startnext sn
cross apply ( select top 1 e.enddate
from data e
where e.id = sn.id
and e.startdate >= sn.startdate
and (e.startdate < sn.startdate_next or sn.startdate_next is null)
order by e.enddate desc ) e
order by sn.id,
sn.startdate;
Result
id startdate enddate
-- ---------- ----------
1 2019-01-21 2019-01-27
1 2019-01-29 2019-02-02
Fiddle to see build up of solution and intermediate CTE results.