Find the maximum consecutive years for each ID's in a table(Oracle SQL)

Question

I am trying to solve a problem of how to find the maximum count of consecutive years in a series of records. In the following example:

ID  Year
1 1993
1 1994
1 19         


        

Answer 1

Try:

with cte as
(select t.id, t.year, d.d, row_number() over (partition by t.id, d.d 
                                              order by t.year) rn
 from (select -1 d from dual union all select 1 d from dual) d
 cross join my_table t 
 where not exists
       (select null
        from my_table o
        where t.id = o.id and t.year = o.year-d.d) )
select s.id, max(e.year-s.year)+1 year_count
from cte s
join cte e on s.id = e.id and s.rn = e.rn and e.d=1
where s.d=-1
group by s.id

SQLFiddle here.