Find non consecutive date ranges

Question

i want to find if some of all the consecutive date ranges has gap between. Some of the dates are not consecutive, in this case it will return the RowId of the single range.

Table Name: Subscriptions

RowId	ClientId	Status	StartDate	EndDate
1	1	1	01/01/2022	02/01/2022
2	1	1	03/01/2022	04/01/2022
3	1	1	12/01/2022	15/01/2022
4	2	1	03/01/2022	06/01/2022

i want a sql statement to find RowId of non consecutive ranges for each client and status in (1,3) (example of result)

RowId
3

I want to solve the problem using SQL only. thanks

Answer 1

One way you could do this is to use Lag (or lead ) to identify gaps in neighbouring rows' date ranges and take the top N rows where the gap exceeds 1 day.

select top (1) with ties rowId 
from t
where status in (1,3)
order by 
  case when DateDiff(day, lag(enddate,1,enddate) 
    over(partition by clientid order by startdate), startdate) >1 
  then 0 else 1 end;

Answer 2

You can detect gaps with LAG() and mark them. Then, it's easy to filter out the rows. For example:

select *
from (
  select *,
    case when dateadd(day, -1, start_date) >
       lag(end_date) over(partition by client_id order by start_date) 
    then 1 else 0 end as i
  from t
) x
where i = 1

Or simpler...

select *
from (
  select *,
    lag(end_date) over(partition by client_id order by start_date) as prev_end
  from t
) x
where dateadd(day, -1, start_date) > prev_end