Ignoring rows within daterange - sql-server

Question

I have the following data:
CREATE TABLE SampleData
(
orderid int,
[name] nvarchar(1),
[date] date
);
INSERT INTO SampleData
VALUES
(1, 'a', '2017-01-01'),
(2, 'a', '2017-01-05'),
(3, 'a', '2017-02-01'),
(4, 'a', '2017-04-01'),
(5, 'a', '2017-10-01'),
(6, 'b', '2017-04-01');
I need to retrieve each new order according to the following rules:
The first date for a name is the 'current order' for that name
Orders with the same name, but less than 3 months difference with the 'current order' is considered the same order and needs to be ignored
3 months or more difference with the 'current' order is considered a new order and is now the 'current order' (in the SampleData orderid 1 and 4 need to be compared instead of 3 and 4, because 3 is not the current order)
If the name and date are the same, then the row with the lowest orderid is the superior order
So with the sample data I need the following result:
id name, date
1 a 2017-01-01
4 a 2017-04-01
5 a 2017-10-01
6 b 2017-04-01
I tried several approaches, but without success. Any idea's on how I can achieve this?

Answer 1

Below is a quick fix solution that can be built upon if your code scales beyond the sample data provided. I will state beforehand that this isn't the prettiest solution but it does return the result set you indicated you were after.
If anything, you may want to consider looking into T-SQL Window Functions as well as Analytic Functions. I will advice that that they don't play well with all datatypes.
My goal with the solution below was to rank the rows while partitioning by name and order by the date field. Thus you have something similar to your order id but the rank is specific to the customer who placed the order.
I'll do my best to answer any questions:
if object_id('tempdb..#tmp_SampleData','u') is not null
drop table #tmp_SampleData
CREATE TABLE #tmp_SampleData
(
orderid int,
[name] nvarchar(1),
[date] date
);
INSERT INTO #tmp_SampleData
VALUES
(1, 'a', '2017-01-01'),
(2, 'a', '2017-01-05'),
(3, 'a', '2017-02-01'),
(4, 'a', '2017-04-01'),
(5, 'a', '2017-10-01'),
(6, 'b', '2017-04-01');
if object_id('tempdb..#tmp_iter','u') is not null
drop table #tmp_iter
select
orderid
,name
,date
,rank() over (partition by name order by date) [Rank]
,lag(orderid,1,0) over (partition by name order by date) [LagRank]
--,rank() over (partition by name order by date desc) [ReverseRank]
into #tmp_Iter
from #tmp_SampleData
if object_id('tempdb..#tmp_final','u') is not null
drop table #tmp_final
select
i.orderid
,i.name
,i.date
,datediff(month,i.date,i2.date) [MonthsPassed]
into #tmp_final
from #tmp_Iter i
left join #tmp_Iter i2
on i.Rank = i2.LagRank
select *
from #tmp_final
where 1=1
and MonthsPassed > 3
or MonthsPassed = 0
or MonthsPassed < 0
or MonthsPassed is null

Answer 2

#SQLUser44, thanks for your input. Unfortunately your code is not working. The result for the table below should be orderid's 1,6,7,8 and 9. Yours results in 1,2,3,5,6,7,8 and 9.
INSERT INTO #tmp_SampleData
VALUES
(1,'a','2017-01-01'),
(2,'a','2017-01-08'),
(3,'a','2017-05-01'),
(4,'a','2017-01-05'),
(5,'a','2017-02-01'),
(6,'b','2017-01-01'),
(7,'b','2017-09-01'),
(8,'c','2017-10-01'),
(9,'a','2017-04-01');
I came up with the following that works, but I think it will lack performance...
if object_id('tempdb..#tmp_SampleData','u') is not null
drop table #tmp_SampleData
CREATE TABLE #tmp_SampleData
(
orderid int,
[name] nvarchar(1),
[date] date
);
INSERT INTO #tmp_SampleData
VALUES
(1,'a','2017-01-01'),
(2,'a','2017-01-08'),
(3,'a','2017-05-01'),
(4,'a','2017-01-05'),
(5,'a','2017-02-01'),
(6,'b','2017-01-01'),
(7,'b','2017-09-01'),
(8,'c','2017-10-01'),
(9,'a','2017-04-01');
DECLARE Test_Cursor CURSOR FOR
SELECT * FROM #tmp_SampleData ORDER BY [name], [date];
OPEN Test_Cursor;
DECLARE #orderid int;
DECLARE #name nvarchar(255);
DECLARE #date date;
FETCH NEXT FROM Test_Cursor INTO #orderid, #name, #date;
DECLARE #current_date date = #date;
DECLARE #current_name nvarchar(255) = #name;
DECLARE #listOfIDs TABLE (orderid int);
INSERT #listOfIDs values(#orderid);
WHILE ##FETCH_STATUS = 0
BEGIN
IF(#name = #current_name AND DATEDIFF(MONTH, #current_date, #date) >= 3)
BEGIN
SET #current_date = #date
INSERT #listOfIDs values(#orderid)
END
IF(#name != #current_name)
BEGIN
SET #current_name = #name
SET #current_date = #date
INSERT #listOfIDs values(#orderid)
END
FETCH NEXT FROM Test_Cursor INTO #orderid, #name, #date;
END;
CLOSE Test_Cursor;
DEALLOCATE Test_Cursor;
SELECT * FROM #tmp_SampleData WHERE orderid IN (SELECT orderid FROM #listOfIDs);
Better performing alternatives are very welcome!