Gaps and islands SQL error

Question

Trying to run a query to identify starts and stops for the gaps and islands in my table. I'm applying a query that I think will work for my data set but I cannot get to run properly. I am getting a conversion error when I run this code:

select start, stop 
from (
select m.API_WellNo + 1 as start,
    (select min(API_WellNo) - 1 
    from tblWellMaster x 
    where x.API_WellNo > m.API_WellNo) as stop
from tblWellMaster m    left outer join tblWellMaster r on m.API_WellNo = r.API_WellNo - 1
where r.API_WellNo is null
  ) as x
where stop is not null;

Here is the error I get: The conversion of the nvarchar value '31003022850000' overflowed an int column.

I can't figure out where this int column is coming from because my API_WellNo is an nvarchar(14)

The number is one of the id's making up the sequence that I am trying to find the gaps/islands in, any help is much appreciated, thank you

Answer 1

Try This:

with cte as (
  select start = (cast(m.API_WellNo as bigint) + 1)
      , [stop] = ca.[stop]
    from tblWellMaster m    
      cross apply (
        select top 1 [stop]=(cast(x.API_WellNo as bigint) -1)
          from tblWellMaster x 
          where x.API_WellNo > m.API_WellNo
          order by x.API_WellNo
        ) as ca
    where not exists (
      select 1 
        from tblWellMaster r 
        where cast(m.API_WellNo as bigint)  = (cast(r.API_WellNo as bigint)  - 1))
  )
  select start, [stop] 
    from cte 
    where [stop] is not null;