SQL: Earliest Date After Latest Null If Exists - sql

Question

Using T-Sql I am looking to return the min date after the latest null if one exists and simply the min date on any products where there are no nulls.
Table:
DateSold Product
12/31/2012 A
1/31/2013
2/28/2013 A
3/31/2013 A
4/30/2013 A
5/31/2013
6/30/2013 A
7/31/2013 A
8/31/2013 A
9/30/2013 A
12/31/2012 B
1/31/2013 B
2/28/2013 B
3/31/2013 B
4/30/2013 B
5/31/2013 B
6/30/2013 B
7/31/2013 B
8/31/2013 B
9/30/2013 B
For product “A” 6/30/2013 is the desired return while for product “B” 12/31/2012 is desired.
Result:
MinDateSold Product
6/30/2013 A
12/31/2012 B
Any solutions will greatly be appreciated. Thank you.

Answer 1

This does it for me, if there's a GROUP involved, otherwise how do you know whether the NULLs are in the run of A or B products? I realise this may not be exactly what you're after, but I hope it helps anyway.
WITH DATA_IN AS (
SELECT 1 as grp,
convert(DateTime,'12/31/2012') as d_Date,
'A' AS d_ch
UNION ALL
SELECT 1, '1/31/2013', NULL UNION ALL
SELECT 1, '2/28/2013', 'A' UNION ALL
SELECT 1, '3/31/2013', 'A' UNION ALL
SELECT 1, '4/30/2013', 'A' UNION ALL
SELECT 1, '5/31/2013', NULL UNION ALL
SELECT 1, '6/30/2013', 'A' UNION ALL
SELECT 1, '7/31/2013', 'A' UNION ALL
SELECT 1, '8/31/2013', 'A' UNION ALL
SELECT 1, '9/30/2013', 'A' UNION ALL
SELECT 2, '12/31/2012', 'B' UNION ALL
SELECT 2, '1/31/2013', 'B' UNION ALL
SELECT 2, '2/28/2013', 'B' UNION ALL
SELECT 2, '3/31/2013', 'B' UNION ALL
SELECT 2, '4/30/2013', 'B' UNION ALL
SELECT 2, '5/31/2013', 'B' UNION ALL
SELECT 2, '6/30/2013', 'B' UNION ALL
SELECT 2, '7/31/2013', 'B' UNION ALL
SELECT 2, '8/31/2013', 'B' UNION ALL
SELECT 2, '9/30/2013', 'B'
)
SELECT
grp as YourGroup,
(SELECT Min(d_date) -- first date after...
FROM DATA_IN
WHERE d_date>
Coalesce( -- either the latest NULL
(SELECT max(d_Date)
FROM DATA_IN d2
WHERE d2.grp=d1.grp AND d2.d_ch IS NULL
)
, '1/1/1901' -- or a base date if no NULLs
)
) as MinDateSold
FROM DATA_IN d1
GROUP BY grp
Results :
1 2013-06-30 00:00:00.000
2 2012-12-31 00:00:00.000

Answer 2

One approach to this is to count the number of NULL values that appear before a given row for a given value. This divides the ranges into groups. For each group, take the minimum date. And, find the largest minimum date for each product:
select product, minDate
from (select product, NumNulls, min(DateSold) as minDate,
row_number() over (partition by product order by min(DateSold) desc
) as seqnum
from (select t.*,
(select count(*)
from table t2
where t2.product is null and t2.DateSold <= t.DateSold
) as NumNulls
from table t
) t
group by Product, NumNUlls
) t
where seqnum = 1;
In your data, there is no mixing of different products in a range, so this query sort of assumes that is true as well.