Group by numbers that are in sequence - sql

Question

I have some data like this:
row id
1 1
2 36
3 37
4 38
5 50
6 51
I would like to query it to look like this:
row id group
1 1 1
2 36 2
3 37 2
4 38 2
5 50 3
6 51 3
... so that I can GROUP BY where the numbers are consecutively sequential.
Also, looping/cursoring is out of the question since I'm working with a pretty large set of data, thanks.

Answer 1

;WITH firstrows AS
(
SELECT id, ROW_NUMBER() OVER (ORDER BY id) groupid
FROM Table1 a
WHERE id - 1 NOT IN (SELECT b.id FROM Table1 b)
)
SELECT id,
(
SELECT MAX(b.groupid)
FROM firstrows b
WHERE b.id <= a.id
) groupid
FROM Table1 a

Answer 2

with
data(row, id) as (
select *
from (
values
(1,1)
,(2,36)
,(3,37)
,(4,38)
,(5,50)
,(6,51)
) as foo(row, id)
),
anchor(row, id) as (
select row, id
from data d1
where not exists(select 0 from data d2 where d2.id = d1.id - 1)
)
select d1.*, dense_rank() over(order by foo.id) as thegroup
from
data d1
cross apply (select max(id) from anchor where anchor.id <= d1.id) as foo(id)
order by
d1.row
;

Answer 3

This solution does more work that is strictly necessary on the basis that there may be gaps in the sequence of row values, and on the assumption that those gaps should be ignored.
Set up test data:
DECLARE #table TABLE
(ROW INT,
id INT
)
INSERT #table
SELECT 1,1
UNION SELECT 2,36
UNION SELECT 3,37
UNION SELECT 4,38
UNION SELECT 5,50
UNION SELECT 6,51
Output query
;WITH grpCTE
AS
(
SELECT ROW, id,
ROW_NUMBER() OVER (ORDER BY ROW
) AS rn
FROM #table
)
,recCTE
AS
(
SELECT ROW, id, rn, 1 AS grp
FROM grpCTE
WHERE rn = 1
UNION ALL
SELECT g.row, g.id, g.rn, CASE WHEN g.id = r.id + 1 THEN r.grp ELSE r.grp + 1 END AS grp
FROM grpCTE AS g
JOIN recCTE AS r
ON g.rn = r.rn + 1
)
SELECT row, id, grp FROM recCTE

Answer 4

create table #temp
(
IDUnique int Identity(1,1),
ID int,
grp int
)
Insert into #temp(ID) Values(1)
Insert into #temp(ID) Values(36)
Insert into #temp(ID) Values(37)
Insert into #temp(ID) Values(38)
Insert into #temp(ID) Values(50)
Insert into #temp(ID) Values(51)
declare #IDUnique int
declare #PreviousUnique int
declare #ID int
declare #grp int
declare #Previous int
declare #Row int
DECLARE #getAccountID CURSOR SET #getAccountID = CURSOR FOR SELECT Row_Number() Over(Order by IDUnique) Row, IDUnique, ID From #temp
OPEN #getAccountID
FETCH NEXT FROM #getAccountID INTO #Row, #IDUnique, #ID
WHILE ##FETCH_STATUS = 0
BEGIN
IF(#Row = 1)
Begin
update #temp set grp = 1 Where IDUnique = #IDUnique
set #Previous = #ID
set #grp = 1
End
Else If (#Previous + 1 = #ID)
Begin
update #temp set grp = #grp Where IDUnique = #IDUnique
set #Previous = #ID
End
Else
Begin
set #Previous = #ID
set #grp = #grp + 1
update #temp set grp = #grp Where IDUnique = #IDUnique
End
FETCH NEXT FROM #getAccountID INTO #Row, #IDUnique, #ID
END
CLOSE #getAccountID
DEALLOCATE #getAccountID
Select * from #temp
Drop Table #temp

Answer 5

Select T.Id, T.Row, groupId as "Group", dr FROM tbrows T
Left Outer Join
(
Select min(id) as groupId,DENSE_RANK() over( order by min(id)) as dr, MIN(row-id) as d, Sum(1) as s FROM tbrows
Group BY (row-id)
) U
On (T.Id >= U.groupId) and (T.Id < U.groupId+U.s)
Order By T.Id