Group rows into sequences using a sliding window on a DateTime column - sql

Question

I have a table that stores timestamped events. I want to group the events into 'sequences' by using 5-min sliding window on the timestamp column, and write the 'sequence ID' (any ID that can distinguish sequences) and 'order in sequence' into another table.
Input - event table:
+----+-------+-----------+
| Id | Name | Timestamp |
+----+-------+-----------+
| 1 | test | 00:00:00 |
| 2 | test | 00:06:00 |
| 3 | test | 00:10:00 |
| 4 | test | 00:14:00 |
+----+-------+-----------+
Desired output - sequence table. Here SeqId is the ID of the starting event, but it doesn't have to be, just something to uniquely identify a sequence.
+---------+-------+----------+
| EventId | SeqId | SeqOrder |
+---------+-------+----------+
| 1 | 1 | 1 |
| 2 | 2 | 1 |
| 3 | 2 | 2 |
| 4 | 2 | 3 |
+---------+-------+----------+
What would be the best way to do it? This is MSSQL 2008, I can use SSAS and SSIS if they make things easier.

Answer 1

CREATE TABLE #Input (Id INT, Name VARCHAR(20), Time_stamp TIME)
INSERT INTO #Input
VALUES
( 1 ,'test','00:00:00' ),
( 2 ,'test','00:06:00' ),
( 3 ,'test','00:10:00' ),
( 4 ,'test','00:14:00' )
SELECT * FROM #Input;
WITH cte AS -- add a sequential number
(
SELECT *,
ROW_NUMBER() OVER(ORDER BY Id) AS sort
FROM #Input
), cte2 as -- find the Id's with a difference of more than 5min
(
SELECT cte.*,
CASE WHEN DATEDIFF(MI, cte_1.Time_stamp,cte.Time_stamp) < 5 THEN 0 ELSE 1 END as GrpType
FROM cte
LEFT OUTER JOIN
cte as cte_1 on cte.sort =cte_1.sort +1
), cte3 as -- assign a SeqId
(
SELECT GrpType, Time_Stamp,ROW_NUMBER() OVER(ORDER BY Time_stamp) SeqId
FROM cte2
WHERE GrpType = 1
), cte4 as -- find the Time_Stamp range per SeqId
(
SELECT cte3.*,cte_2.Time_stamp as TS_to
FROM cte3
LEFT OUTER JOIN
cte3 as cte_2 on cte3.SeqId =cte_2.SeqId -1
)
-- final query
SELECT
t.Id,
cte4.SeqId,
ROW_NUMBER() OVER(PARTITION BY cte4.SeqId ORDER BY t.Time_stamp) AS SeqOrder
FROM cte4 INNER JOIN #Input t ON t.Time_stamp>=cte4.Time_stamp AND (t.Time_stamp <cte4.TS_to OR cte4.TS_to IS NULL);
This code is slightly more complex but it returns the expected output (which Gordon Linoffs solution doesn't...) and it's even slightly faster.

Answer 2

You seem to want things grouped together when they are less than five minutes apart. You can assign the groups by getting the previous time stamp and marking the beginning of a group. You then need to do a cumulative sum to get the group id:
with e as (
select e.*,
(case when datediff(minute, prev_timestamp, timestamp) < 5 then 1 else 0 end) as flag
from (select e.*,
(select top 1 e2.timestamp
from events e2
where e2.timestamp < e.timestamp
order by e2.timestamp desc
) as prev_timestamp
from events e
) e
)
select e.eventId, e.seqId,
row_number() over (partition by seqId order b timestamp) as seqOrder
from (select e.*, (select sum(flag) from e e2 where e2.timestamp <= e.timestamp) as seqId
from e
) e;
By the way, this logic is easier to express in SQL Server 2012+ because the window functions are more powerful.