SQL - Group rows via criteria until exception is found - sql

Question

I am trying to add a Group column to a data set based on some criteria. For a simple example:
╔════╦══════╗
║ ID ║ DATA ║
╠════╬══════╣
║ 1 ║ 12 ║
║ 2 ║ 20 ║
║ 3 ║ 3 ║
║ 4 ║ 55 ║
║ 5 ║ 11 ║
╚════╩══════╝
Let's say our criteria is that the Data should be greater than 10. Then the result should be similar to:
╔════╦══════╦═══════╗
║ ID ║ DATA ║ GROUP ║
╠════╬══════╬═══════╣
║ 1 ║ 12 ║ 1 ║
║ 2 ║ 20 ║ 1 ║
║ 3 ║ 3 ║ 2 ║
║ 4 ║ 55 ║ 3 ║
║ 5 ║ 11 ║ 3 ║
╚════╩══════╩═══════╝
So, all the rows that satisfied the criteria until an exception to the criteria occurred became part of a group. The numbering of the group doesn't necessarily need to follow this pattern, I just felt like this was a logical/simple numbering to explain the solution I am looking for.

Answer 1

You can calculate the group identifier by finding each row where data <= 10. Then, the group identifier is simply the number of rows where that condition is true, before the given row.
select t.*,
(select count(*)
from t t2
where t2.id <= t.id and
t2.data <= 10
) as groupId
from t;
SQL Server 2012 has cumulative sum syntax. The statement would be simpler in that database:
select t.*,
sum(case when t2.data <= 10) over (order by id) as groupId
from t;
EDIT:
The above does not take into account that the values less than 10 are in their own group. The logic above is that they start a new group.
The following assigns a group id with this constraint:
select t.*,
((select 2*count(*)
from t t2
where t2.id < t.id and
t2.data <= 10
) + (case when t.id <= 10 then 1 else 0 end)
) as groupId
from t;

Answer 2

This can be done easily with a recursive query:
;WITH CTE
AS (SELECT *,
1 AS [GROUP]
FROM TABLEB
WHERE ID = 1
UNION ALL
SELECT T1.ID,
T1.DATA,
CASE
WHEN T1.DATA < 10 THEN T2.[GROUP] + 1
ELSE T2.[GROUP]
END [GROUP]
FROM TABLEB T1
INNER JOIN CTE T2
ON T1.ID = T2.ID + 1)
SELECT *
FROM CTE
A working example can be found on SQL Fiddle.
Good Luck!