Find max continuous period for multiple enrollment in SQL Server - sql

Question

I'm trying to find max number of continues days for each Cust_Nbr. For each year he can have multiple ones with or without breaks,in example below Cust has 3 PolicNo and for this case I need to find that max days = 5 (like for PolicNo = 1) and max=2 for other. I did try to work with some numbers, finished with the table like below but not sure how I can go thru all this for each by Cust_Nbr to catch any break. Appreciate your leads. I also pasted test data. Still have errors in my code .
Drop table if exists #T;
CREATE TABLE #t (Cust_Nbr int, PolicNo int, ENR_START Date, ENR_END DATE, DD Date, DayNum int, DayNum_Prev Int)
insert #t values
(11111, 1, '11/27/2019', '12/1/2019', '11/27/2019', 331, 0),
(11111, 1, '11/27/2019', '12/1/2019', '11/28/2019', 332, 331),
(11111, 1, '11/27/2019', '12/1/2019', '11/29/2019', 333, 332),
(11111, 1, '11/27/2019', '12/1/2019', '11/30/2019', 334, 333),
(11111, 1, '11/27/2019', '12/1/2019', '12/1/2019', 335, 334),
(11111, 22,'12/8/2019', '12/10/2019', '12/8/2019', 342, 335),
(11111, 22, '12/8/2019', '12/10/2019', '12/9/2019', 343, 342),
(11111, 22, '12/8/2019', '12/10/2019', '12/10/2019', 344, 343),
(11111, 333, '12/26/2019', '12/29/2019', '12/26/2019', 360, 344),
(11111, 333, '12/26/2019', '12/29/2019', '12/27/2019', 361, 360),
(11111, 333, '12/26/2019', '12/29/2019', '12/28/2019', 362, 361),
(11111, 333, '12/26/2019', '12/29/2019', '12/29/2019', 363, 362),
(999999, 90, '12/8/2019', '12/9/2019', '12/8/2019', 342, 0),
(999999, 90, '12/8/2019', '12/9/2019', '12/9/2019', 343, 342)
Select t.* , Days_Max = ( SELECT TOP 1 Cust_Nbr, COUNT(*)
FROM #t t2
WHERE t2.Cust_Nbr = t.Cust_Nbr
)
FROM #t t

Answer 1

Looking at the example you can actually do this with below query.
;WITH CTE1 AS
(
SELECT Cust_Nbr,
PolicNo,
COUNT(DayNum_Prev) as max_days,
ROW_NUMBER() OVER (PARTITION BY Cust_Nbr ORDER BY COUNT(DayNum_Prev) DESC) RN
FROM #t
GROUP BY Cust_Nbr,PolicNo
)
SELECT Cust_Nbr ,PolicNo,max_days FROM CTE1 WHERE RN=1
Or using your logic as below
;WITH CTE2 AS
(
SELECT *,ROW_NUMBER() OVER (ORDER BY Cust_Nbr,PolicNo) Rnk ,
CASE WHEN DayNum_Prev=DayNum-1 THEN 0 ELSE 1 END cols
FROM #t
)
,CTE3 AS
(
SELECT *,SUM(cols) OVER(ORDER BY Rnk) Grouper FROM CTE2
)
,CTE4 AS
(
SELECT Cust_Nbr,PolicNo,count(*) MAX_DAYS,
ROW_NUMBER() OVER (PARTITION BY Cust_Nbr ORDER BY COUNT(*) DESC) RN
FROM CTE3
GROUP BY Cust_Nbr,PolicNo,grouper
)
SELECT CUST_NBR,POLICNO,MAX_DAYS FROM CTE4 WHERE RN =1
Check Demo Here

Answer 2

Below solution is in PostgreSQL but you may apply similar logic in tsql. here is the demo.
select
cust_nbr,
policNo,
total
from
(
select
cust_nbr,
policNo,
count(rnk) as total,
dense_rank() over (partition by cust_nbr order by count(rnk) desc) as nrnk
from
(
select
cust_nbr,
policNo,
(dd - '2000-01-01'::date
- row_number() over (partition by cust_nbr, policNo order by dd)) as rnk
from myTable
) val
group by
cust_nbr,
policNo,
rnk
) res
where nrnk = 1
Output:
*-----------------------*
|cust_nbr policno total |
*-----------------------*
|11111 1 5 |
|999999 99 2 |
*-----------------------*