SQL Server 2019 (Linux)

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CREATE TABLE EventLog 
(
  EventID INT
, EventName VARCHAR(50) NOT NULL
, EventStartDateTime DATETIME NOT NULL
, EventEndDateTime   DATETIME NULL 
)


INSERT INTO EventLog(EventID, EventName, EventStartDateTime, EventEndDateTime)
VALUES(100, 'Planting', '20210620 10:34:09 AM','20211018 10:54:49 PM')
 ,(200, 'Foundation', '20200420 10:34:09 AM','20211018 10:54:49 PM')
 ,(300, 'Seeding', '20210410 10:27:19 AM','')
 ,(400, 'Spreading', '20220310 10:24:09 PM','');
 
 CREATE TABLE EventSummary
(  
  EventID INT
, EventName VARCHAR(50) NOT NULL
, [Year] INT
, [MonthName] VARCHAR(25) 
, [Hours] DECIMAL(12,2) 
)
4 rows affected


;WITH CTE AS (
   SELECT EventID,EventName,EventStartDateTime,IIF(EventEndDateTime = '',GETUTCDATE(),EventEndDateTime) EventEndDateTime
   FROM EventLog
   UNION ALL
   SELECT EventID,EventName, DATEADD(month, DATEDIFF(month, 0, DATEADD(month , 1 , EventStartDateTime)), 0) , EventEndDateTime
   FROM CTE 
   WHERE  DATEADD(month, DATEDIFF(month, 0, DATEADD(month , 1 , EventStartDateTime)), 0)  <= EventEndDateTime
)
INSERT INTO EventSummary(EventID,EventName,Year,MonthName,Hours)
SELECT EventID,EventName,YEAR(EventStartDateTime),DATENAME(MONTH,EventStartDateTime),DATEDIFF(second, EventStartDateTime, n_EventStartDateTime) / 3600.0
FROM (
  SELECT EventID,EventName,EventStartDateTime,LEAD(EventStartDateTime,1,EventEndDateTime) OVER(PARTITION BY EventID,EventName ORDER BY EventStartDateTime) n_EventStartDateTime
  FROM CTE
) t1
option (maxrecursion 0)
47 rows affected

SELECT * FROM EventSummary


EventID
EventName
Year
MonthName
Hours


100
Planting
2021
June
253.43

100
Planting
2021
July
744.00

100
Planting
2021
August
744.00

100
Planting
2021
September
720.00

100
Planting
2021
October
430.91

200
Foundation
2020
April
253.43

200
Foundation
2020
May
744.00

200
Foundation
2020
June
720.00

200
Foundation
2020
July
744.00

200
Foundation
2020
August
744.00

200
Foundation
2020
September
720.00

200
Foundation
2020
October
744.00

200
Foundation
2020
November
720.00

200
Foundation
2020
December
744.00

200
Foundation
2021
January
744.00

200
Foundation
2021
February
672.00

200
Foundation
2021
March
744.00

200
Foundation
2021
April
720.00

200
Foundation
2021
May
744.00

200
Foundation
2021
June
720.00

200
Foundation
2021
July
744.00

200
Foundation
2021
August
744.00

200
Foundation
2021
September
720.00

200
Foundation
2021
October
430.91

300
Seeding
2021
April
493.54

300
Seeding
2021
May
744.00

300
Seeding
2021
June
720.00

300
Seeding
2021
July
744.00

300
Seeding
2021
August
744.00

300
Seeding
2021
September
720.00

300
Seeding
2021
October
744.00

300
Seeding
2021
November
720.00

300
Seeding
2021
December
744.00

300
Seeding
2022
January
744.00

300
Seeding
2022
February
672.00

300
Seeding
2022
March
744.00

300
Seeding
2022
April
720.00

300
Seeding
2022
May
744.00

300
Seeding
2022
June
720.00

300
Seeding
2022
July
744.00

300
Seeding
2022
August
221.69

400
Spreading
2022
March
505.60

400
Spreading
2022
April
720.00

400
Spreading
2022
May
744.00

400
Spreading
2022
June
720.00

400
Spreading
2022
July
744.00

400
Spreading
2022
August
221.69

EventID	EventName	Year	MonthName	Hours
100	Planting	2021	June	253.43
100	Planting	2021	July	744.00
100	Planting	2021	August	744.00
100	Planting	2021	September	720.00
100	Planting	2021	October	430.91
200	Foundation	2020	April	253.43
200	Foundation	2020	May	744.00
200	Foundation	2020	June	720.00
200	Foundation	2020	July	744.00
200	Foundation	2020	August	744.00
200	Foundation	2020	September	720.00
200	Foundation	2020	October	744.00
200	Foundation	2020	November	720.00
200	Foundation	2020	December	744.00
200	Foundation	2021	January	744.00
200	Foundation	2021	February	672.00
200	Foundation	2021	March	744.00
200	Foundation	2021	April	720.00
200	Foundation	2021	May	744.00
200	Foundation	2021	June	720.00
200	Foundation	2021	July	744.00
200	Foundation	2021	August	744.00
200	Foundation	2021	September	720.00
200	Foundation	2021	October	430.91
300	Seeding	2021	April	493.54
300	Seeding	2021	May	744.00
300	Seeding	2021	June	720.00
300	Seeding	2021	July	744.00
300	Seeding	2021	August	744.00
300	Seeding	2021	September	720.00
300	Seeding	2021	October	744.00
300	Seeding	2021	November	720.00
300	Seeding	2021	December	744.00
300	Seeding	2022	January	744.00
300	Seeding	2022	February	672.00
300	Seeding	2022	March	744.00
300	Seeding	2022	April	720.00
300	Seeding	2022	May	744.00
300	Seeding	2022	June	720.00
300	Seeding	2022	July	744.00
300	Seeding	2022	August	221.69
400	Spreading	2022	March	505.60
400	Spreading	2022	April	720.00
400	Spreading	2022	May	744.00
400	Spreading	2022	June	720.00
400	Spreading	2022	July	744.00
400	Spreading	2022	August	221.69