Populate a GroupID - sql

Question

Please see the DDL below:
CREATE TABLE #Test (ID)
INSERT INTO #Test values (1)
INSERT INTO #Test values (2)
INSERT INTO #Test values (3)
INSERT INTO #Test values (0)
INSERT INTO #Test values (4)
INSERT INTO #Test values (5)
INSERT INTO #Test values (6)
INSERT INTO #Test values (8)
INSERT INTO #Test values (12)
INSERT INTO #Test values (19)
INSERT INTO #Test values (0)
INSERT INTO #Test values (44)
I am looking for a query that outputs the following (GroupID, ID).
1,1
1,2
1,3
2,4
2,5
2,6
2,8
2,12
2,19
3,44
A row with an ID of 0 splits the groups.
The query will look something like this:
select GroupID = row_number() over (order by (select null)),ID from #Test
The GroupID needs to be split using the rows that have a zero value. The query above just creates a new GroupID for each row.

Answer 1

SQL tables represent unordered sets. So, you cannot do what you want with your data structure, because it has no ordering. However, that is easily fixed by adding an identity column:
CREATE TABLE #Test (
TestId int identity(1, 1) primary key, -- the primary key is not strictly necessary, just my habit with identity columns.
Val int
);
(I took the liberty of renaming your column to val instead of id to avoid confusion.) An identity column captures insertion order.
The the group is calculated as the number of zeros before a given value. In SQL Server 2012+, this is easily done using a cumulative sum:
select t.*,
1 + sum(case when val = 0 then 1 else 0 end) over (order by testid) as groupid
from #test t;
I notice that you don't want zeros in the output, for this purpose, use a subquery after the cumulative sum:
select *
from (select t.*,
1 + sum(case when val = 0 then 1 else 0 end) over (order by testid) as groupid
from #test t
) t
where val <> 0;