How to filter out multiple downtime events in SQL Server? - sql

Question

There is a query I need to write that will filter out multiples of the same downtime event. These records get created at the exact same time with multiple different timestealrs which I don't need. Also, in the event of multiple timestealers for a downtime event I need to make the timestealer 'NULL' instead.
Example table:
Id
TimeStealer
Start
End
Is_Downtime
Downtime_Event
1
Machine 1
2022-01-01 01:00:00
2022-01-01 01:01:00
1
Malfunction
2
Machine 2
2022-01-01 01:00:00
2022-01-01 01:01:00
1
Malfunction
3
NULL
2022-01-01 00:01:00
2022-01-01 00:59:59
0
Operating
What I need the query to return:
Id
TimeStealer
Start
End
Is_Downtime
Downtime_Event
1
NULL
2022-01-01 01:00:00
2022-01-01 01:01:00
1
Malfunction
2
NULL
2022-01-01 00:01:00
2022-01-01 00:59:59
0
Operating

Answer 1

Seems like this is a top 1 row of each group, but with the added logic of making a column NULL when there are multiple rows. You can achieve that by also using a windowed COUNT, and then a CASE expression in the outer SELECT to only return the value of TimeStealer when there was 1 event:
WITH CTE AS(
SELECT V.Id,
V.TimeStealer,
V.Start,
V.[End],
V.Is_Downtime,
V.Downtime_Event,
ROW_NUMBER() OVER (PARTITION BY V.Start, V.[End], V.Is_Downtime,V.Downtime_Event ORDER BY ID) AS RN,
COUNT(V.ID) OVER (PARTITION BY V.Start, V.[End], V.Is_Downtime,V.Downtime_Event) AS Events
FROM(VALUES('1','Machine 1',CONVERT(datetime2(0),'2022-01-01 01:00:00'),CONVERT(datetime2(0),'2022-01-01 01:01:00'),'1','Malfunction'),
('2','Machine 2',CONVERT(datetime2(0),'2022-01-01 01:00:00'),CONVERT(datetime2(0),'2022-01-01 01:01:00'),'1','Malfunction'),
('3','NULL',CONVERT(datetime2(0),'2022-01-01 00:01:00'),CONVERT(datetime2(0),'2022-01-01 00:59:59'),'0','Operating'))V(Id,TimeStealer,[Start],[End],Is_Downtime,Downtime_Event))
SELECT ROW_NUMBER() OVER (ORDER BY ID) AS ID,
CASE WHEN C.Events = 1 THEN C.TimeStealer END AS TimeStealer,
C.Start,
C.[End],
C.Is_Downtime,
C.Downtime_Event
FROM CTE C
WHERE C.RN = 1;