Determine first year of minimum consecutive year range and count of consecutive years - sql

Question

Given the following table,
PersonID Year
---------- ----------
1 1991
1 1992
1 1993
1 1994
1 1996
1 1997
1 1998
1 1999
1 2000
1 2001
1 2002
1 2003
2 1999
2 2000
... ...
Is there a way with a SQL select query to get the first year of the most recent range of consecutive years meeting a minimum number, as well as the total consecutive years? In this case, for 4 year minimum, for personID 1, it would return 1996 and 8.
This will be joined to another table on personID, so the personID is not specific.
Thanks for your help.

Answer 1

You can create islands of years in the cte and check your conditions:
declare #PersonId int = 1, #cnt int = 4
;with cte_numbered as (
select
PersonID,
[Year],
row_number() over(partition by PersonID order by [Year]) as rn
from Table1
), cte_grouped as (
select
PersonID, min([Year]) as [Year], count(*) as cnt
from cte_numbered
group by PersonID, [Year] - rn
)
select top 1 *
from cte_grouped
where PersonId = #PersonId and cnt >= #cnt
order by [Year] desc
sql fiddle demo
You also could do something more optimized, like this
declare #PersonId int = 1, #cnt int = 4
;with cte_numbered as (
select
PersonID,
[Year],
row_number() over(partition by PersonID order by [Year]) as rn
from Table1
where personId = #personId
), cte_grouped as (
select
row_number() over(partition by [year] - rn order by year) as cnt, year
from cte_numbered
)
select top 1 cnt, year - cnt + 1
from cte_grouped
where cnt >= #cnt
order by [Year] desc, cnt desc
sql fiddle demo

Answer 2

Using two CTEs to create row number groupings allows you to group by PersonID and display all personIDs that it applies to:
Declare #MinimumConsecutiveYears int=4
;With YearGroupings as (
Select
PersonID
,year
,row_number() over(partition by personid order by year asc) rown
From #years
)
, ConsecutiveYears as (
Select
PersonID
,min(year) as MinYear
,count(rown) as ConsecutiveYears
,row_number() over(partition by PersonID order by count(rown) desc) rown
From YearGroupings
Group By PersonID,year-rown
Having Count(rown)>#MinimumConsecutiveYears
)
Select PersonID,MinYear,ConsecutiveYears
From ConsecutiveYears
Where Rown=1
Alternatively, without CTEs:
Declare #MinimumConsecutiveYears int=4
Select
PersonID
,year
,row_number() over(partition by personid order by year asc) rown
Into #YearGroupings
From #years
Select
PersonID
,min(year) as MinYear
,count(rown) as ConsecutiveYears
,row_number() over(partition by PersonID order by count(rown) desc) rown
Into #ConsecutiveYears
From YearGroupings
Group By PersonID,year-rown
Having Count(rown)>#MinimumConsecutiveYears
Select PersonID,MinYear,ConsecutiveYears
From #ConsecutiveYears
Where Rown=1

Answer 3

try this:
declare #minnumber int
set #minnumber = 4
declare #personid int
set #personid = 0
select orig.[PersonID], min(orig.[Year]) as FirstYear ,count(*) as TCYears
from --add rownumber, sorted by year column
(
SELECT ROW_NUMBER()
OVER (Partition by [PersonID] ORDER BY [Year]) AS Row,*
from Table1
where PersonID = #personid
) orig
where orig.PersonID = #personid
and orig.Row > #minnumber --
group by orig.PersonID