Incremental Group BY - sql

Question

How I can achieve incremental grouping in query ?
I need to group by all the non-zero values into different named groups.
Please help me write a query based on columns date and subscribers.

Answer 1

If you have SQL Server 2012 or newer, you can use few tricks with windows functions to get this kind of grouping without cursors, with something like this:
select
Date, Subscribers,
case when Subscribers = 0 then 'No group'
else 'Group' + convert(varchar, GRP) end as GRP
from (
select
Date, Subscribers,
sum (GRP) over (order by Date asc) as GRP
from (
select
*,
case when Subscribers > 0 and
isnull(lag(Subscribers) over (order by Date asc),0) = 0 then 1 else 0 end as GRP
from SubscribersCountByDay S
) X
) Y
Example in SQL Fiddle

Answer 2

In general I advocate AGAINST cursors but in this case it ill not hurt since it ill iterate, sum up and do the conditional all in one pass.
Also note I hinted it with FAST_FORWARD to not degrade performance.
I'm guessing you do want what #HABO commented.
See the working example below, it just sums up until find a ZERO, reset and starts again. Note the and #Sum > 0 handles the case where the first row is ZERO.
create table dbo.SubscribersCountByDay
(
[Date] date not null
,Subscribers int not null
)
GO
insert into dbo.SubscribersCountByDay
([Date], Subscribers)
values
('2015-10-01', 1)
,('2015-10-02', 2)
,('2015-10-03', 0)
,('2015-10-04', 4)
,('2015-10-05', 5)
,('2015-10-06', 0)
,('2015-10-07', 7)
GO
declare
#Date date
,#Subscribers int
,#Sum int = 0
,#GroupId int = 1
declare #Result as Table
(
GroupName varchar(10) not null
,[Sum] int not null
)
declare ScanIt cursor fast_forward
for
(
select [Date], Subscribers
from dbo.SubscribersCountByDay
union
select '2030-12-31', 0
) order by [Date]
open ScanIt
fetch next from ScanIt into #Date, #Subscribers
while ##FETCH_STATUS = 0
begin
if (#Subscribers = 0 and #Sum > 0)
begin
insert into #Result (GroupName, [Sum]) values ('Group ' + cast(#GroupId as varchar(6)), #Sum)
set #GroupId = #GroupId + 1
set #Sum = 0
end
else begin
set #Sum = #Sum + #Subscribers
end
fetch next from ScanIt into #Date, #Subscribers
end
close ScanIt
deallocate ScanIt
select * from #Result
GO
For the OP: Please next time write the table, just posting an image is lazy

Answer 3

In a version of SQL Server modern enough to support CTEs you can use the following cursorless query:
-- Sample data.
declare #SampleData as Table ( Id Int Identity, Subscribers Int );
insert into #SampleData ( Subscribers ) values
-- ( 0 ), -- Test edge case when we have a zero first row.
( 200 ), ( 100 ), ( 200 ),
( 0 ), ( 0 ), ( 0 ),
( 50 ), ( 50 ), ( 12 ),
( 0 ), ( 0 ),
( 43 ), ( 34 ), ( 34 );
select * from #SampleData;
-- Run the query.
with ZerosAndRows as (
-- Add IsZero to indicate zero/non-zero and a row number to each row.
select Id, Subscribers,
case when Subscribers = 0 then 0 else 1 end as IsZero,
Row_Number() over ( order by Id ) as RowNumber
from #SampleData ),
Groups as (
-- Add a group number to every row.
select Id, Subscribers, IsZero, RowNumber, 1 as GroupNumber
from ZerosAndRows
where RowNumber = 1
union all
select FAR.Id, FAR.Subscribers, FAR.IsZero, FAR.RowNumber,
-- Increment GroupNumber only when we move from a non-zero row to a zero row.
case when Groups.IsZero = 1 and FAR.IsZero = 0 then Groups.GroupNumber + 1 else Groups.GroupNumber end
from ZerosAndRows as FAR inner join Groups on Groups.RowNumber + 1 = FAR.RowNumber
)
-- Display the results.
select Id, Subscribers,
case when IsZero = 0 then 'no group' else 'Group' + Cast( GroupNumber as VarChar(10) ) end as Grouped
from Groups
order by Id;
To see the intermediate results just replace the final select with select * from FlagsAndRows or select * from Groups.