SQL Server iterating through time series data - sql

Question

I am using SQL Server and wondering if it is possible to iterate through time series data until specific condition is met and based on that label my data in other table?
For example, let's say I have a table like this:
Id Date Some_kind_of_event
+--+----------+------------------
1 |2018-01-01|dsdf...
1 |2018-01-06|sdfs...
1 |2018-01-29|fsdfs...
2 |2018-05-10|sdfs...
2 |2018-05-11|fgdf...
2 |2018-05-12|asda...
3 |2018-02-15|sgsd...
3 |2018-02-16|rgw...
3 |2018-02-17|sgs...
3 |2018-02-28|sgs...
What I want to get, is to calculate for each key the difference between two adjacent events and find out if there exists difference > 10 days between these two adjacent events. In case yes, I want to stop iterating for that specific key and put label 'inactive', otherwise 'active' in my other table. After we finish with one key, we start with another.
So for example id = 1 would get label 'inactive' because there exists two dates which have difference bigger that 10 days. The final result would be like that:
Id Label
+--+----------+
1 |inactive
2 |active
3 |inactive
Any ideas how to do that? Is it possible to do it with SQL?

Answer 1

When working with a DBMS you need to get away from the idea of thinking iteratively. Instead you need to try and think in sets. "Instead of thinking about what you want to do to a row, think about what you want to do to a column."
If I understand correctly, is this what you're after?
CREATE TABLE SomeEvent (ID int, EventDate date, EventName varchar(10));
INSERT INTO SomeEvent
VALUES (1,'20180101','dsdf...'),
(1,'20180106','sdfs...'),
(1,'20180129','fsdfs..'),
(2,'20180510','sdfs...'),
(2,'20180511','fgdf...'),
(2,'20180512','asda...'),
(3,'20180215','sgsd...'),
(3,'20180216','rgw....'),
(3,'20180217','sgs....'),
(3,'20180228','sgs....');
GO
WITH Gaps AS(
SELECT *,
DATEDIFF(DAY,LAG(EventDate) OVER (PARTITION BY ID ORDER BY EventDate),EventDate) AS EventGap
FROM SomeEvent)
SELECT ID,
CASE WHEN MAX(EventGap) > 10 THEN 'inactive' ELSE 'active' END AS Label
FROM Gaps
GROUP BY ID
ORDER BY ID;
GO
DROP TABLE SomeEvent;
GO
This assumes you are using SQL Server 2012+, as it uses the LAG function, and SQL Server 2008 has less than 12 months of any kind of support.

Answer 2

Try this. Note, replace #MyTable with your actual table.
WITH Diffs AS (
SELECT
Id
,DATEDIFF(DAY,[Date],LEAD([Date],1,0) OVER (ORDER BY [Id], [Date])) Diff
FROM #MyTable)
SELECT
Id
,CASE WHEN MAX(Diff) > 10 THEN 'Inactive' ELSE 'Active' END
FROM Diffs
GROUP BY Id

Answer 3

Just to share another approach (without a CTE).
SELECT
ID
, CASE WHEN SUM(TotalDays) = (MAX(CNT) - 1) THEN 'Active' ELSE 'Inactive' END Label
FROM (
SELECT
ID
, EventDate
, CASE WHEN DATEDIFF(DAY, EventDate, LEAD(EventDate) OVER(PARTITION BY ID ORDER BY EventDate)) < 10 THEN 1 ELSE 0 END TotalDays
, COUNT(ID) OVER(PARTITION BY ID) CNT
FROM EventsTable
) D
GROUP BY ID
The method is counting how many records each ID has, and getting the TotalDays by date differences (in days) between the current the next date, if the difference is less than 10 days, then give me 1, else give me 0.
Then compare, if the total days equal the number of records that each ID has (minus one) would print Active, else Inactive.
This is just another approach that doesn't use CTE.