Sql query to get unique date based on month - sql

Question

I am working on pulling some data from a table.
declare #SampleData as Table(Id int, ContactId int, Item varchar(25),CreatedOn date)
insert into #SampleData
VALUES(100,2500,'Some item name 1212', '9/5/2020'),
(104,2500,'Some item name 2232', '9/15/2020'),
(109,2500,'Some item name 3434', '9/20/2020'),
(112,3000,'Some item name 5422', '8/1/2020'),
(132,3000,'Some item name 344', '9/5/2020'),
(134,3000,'Some item name 454', '9/15/2020'),
(139,3500,'Some item name 6455', '7/5/2020'),
(146,3500,'Some item name 546', '8/5/2020'),
(142,3500,'Some item name 867', '9/5/2020'),
(149,3500,'Some item name 677', '9/15/2020'),
(150,3500,'Some item name 888', '9/19/2020')
The logic here is so that you can find new contact id each month (so logic is if same contact dont have any record in last 28 days from 1st of that month, it consider as new contact)
When you have two date periods, this is easy to do so you can exclude the records you want as below
SELECT *
FROM #SampleData
WHERE CreatedOn> = #FromDate
and CreatedOn <=#Date
and ContactId not in (SELECT ContactId
FROM #SampleData
WHERE CreatedOn >= DateAdd(Day, -28,#FromDate)
AND CreatedOn < #FromDate)
What I want is to pre-populate this data without having parameters to a some table so that user can use.
In this example data, I am expecting contact 3500 for July, 3000 for August and 2500&3000 for September.
Also it need to display only record per contact and not duplicate.
DECLARE #From date,
#To date
DECLARE date_cursor CURSOR FOR
select distinct DATEADD(month, DATEDIFF(month, 0, CreatedOn), 0) FromDate,EOMONTH(CreatedOn) ToDate
from #SampleData
OPEN date_cursor
FETCH NEXT FROM date_cursor INTO #From,#To
WHILE ##FETCH_STATUS = 0
BEGIN
SELECT *
FROM (
SELECT DISTINCT ContactId,#From 'From Date', #To 'To Date'
FROM #SampleData D
WHERE D.CreatedOn>= #From AND D.CreatedOn <= #To
AND ContactId NOT IN (SELECT ContactId
FROM #SampleData
WHERE CreatedOn >= DateAdd(Day, -28,#From)
AND CreatedOn < #From)) ContactData
OUTER APPLY (
--pick first row for the contact as per the period
SELECT TOP 1 *
FROM #SampleData D
WHERE D.ContactId = ContactData.ContactId
AND D.CreatedOn >= ContactData.[From Date]
AND D.CreatedOn < ContactData.[To Date]
ORDER BY CreatedOn
) Records
FETCH NEXT FROM date_cursor INTO #From,#To
END
CLOSE date_cursor
DEALLOCATE date_cursor
Result
ContactId From Date To Date Id Item CreatedOn
3500 01/07/2020 31/07/2020 139 Some item name 6455 05/07/2020
3000 01/08/2020 31/08/2020 112 Some item name 5422 01/08/2020
2500 01/09/2020 30/09/2020 100 Some item name 1212 05/09/2020
3000 01/09/2020 30/09/2020 132 Some item name 344 05/09/2020
I would like to get rid of cursor, is there any possibility

Answer 1

You can assign a grouping to the contacts by using lag() and comparing the rows:
select sd.*,
sum(case when prev_createdon > dateadd(day, -28, createdon) then 0 else 1 end) over
(partition by contactid order by createdon) as grouping
from (select sd.*,
lag(createdon) over (partition by contactid order by createdon) as prev_createdon
from SampleData sd
) sd;
If you just want the first row in a series of adjacent records, then:
select sd.*
from (select sd.*,
lag(createdon) over (partition by contactid order by createdon) as prev_createdon
from SampleData sd
) sd
where prev_createdon < dateadd(day, -28, createdon) or prev_createdon is null;
Here is a db<>fiddle.
EDIT:
Based on the revised question, you want to summarize by group. You an do this using:
select contactid, min(createdon), max(createdon), min(id),
max(case when seqnum = 1 then item end) as item
from (select sd.*,
row_number() over (partition by contactid, grouping order by createdon) as seqnum
from (select sd.*,
sum(case when prev_createdon > dateadd(day, -28, createdon) then 0 else 1 end) over
(partition by contactid order by createdon) as grouping
from (select sd.*,
lag(createdon) over (partition by contactid order by createdon) as prev_createdon
from SampleData sd
) sd
) sd
) sd
group by contactid, grouping;
I updated the DB fiddle to have this as well.