Oracle: splitting time range into days and calculation of duration - oracle

Question

I'm developing code calculation service availability based on events, so I need to split events into daily "sub-events" and calculate duration of then.
So as input I have set of events like (EVENT_ID, START_TIME, END_TIME):
'event1';2021-05-01 12:30;2021-05-01 13:00
'event2';2021-05-03 10:55;2021-05-05 12:01
As output I'd like to get (EVENT_ID, DAY, DURATION_MINUTES):
'event1'; 2021-05-01; 30
'event2'; 2021-05-03; 785
'event2'; 2021-05-04; 1440
'event2'; 2021-05-05; 721
I can get it using procedures and cursor but this is not effective (the events database is quite big), so is there a way to do it using oracle sql query ? Any idea?

Answer 1

You appear to want a recursive query:
WITH days ( event_id, day, start_time, end_time ) AS (
SELECT event_id,
TRUNC( start_time ),
start_time,
end_time
FROM table_name
UNION ALL
SELECT event_id,
day + INTERVAL '1' DAY,
start_time,
end_time
FROM days
WHERE day + INTERVAL '1' DAY < end_time
)
SELECT event_id,
day,
ROUND(
(
LEAST(end_time, day + INTERVAL '1' DAY)
- GREATEST(start_time, day)
) * 24 * 60
) AS duration_minutes
FROM days
Which, for the sample data:
CREATE TABLE table_name ( event_id, start_time, end_time ) AS
SELECT 'event1', DATE '2021-05-01' + INTERVAL '12:30' HOUR TO MINUTE, DATE '2021-05-01' + INTERVAL '13:00' HOUR TO MINUTE FROM DUAL UNION ALL
SELECT 'event2', DATE '2021-05-03' + INTERVAL '10:55' HOUR TO MINUTE, DATE '2021-05-05' + INTERVAL '12:01' HOUR TO MINUTE FROM DUAL;
Outputs:
EVENT_ID
DAY
DURATION_MINUTES
event1
2021-05-01
30
event2
2021-05-03
785
event2
2021-05-04
1440
event2
2021-05-05
721
db<>fiddle here

Answer 2

If your Oracle version is 12 or higher, you can use a lateral join (in any of several equivalent formulations/syntaxes) to make the query faster. For example (using the table set up in MT0's answer):
select event_id, day, round(1440 * duration_days) as duration_minutes
from table_name cross join lateral
( select trunc(start_time) + level - 1 as day,
case when level = 1 and connect_by_isleaf = 1
then end_time - start_time
when level = 1 then 1 - (start_time - trunc(start_time))
when connect_by_isleaf = 1 then end_time - trunc(end_time)
else 1 end as duration_days
from dual
connect by level <= 1 + trunc(end_time) - trunc(start_time)
)
where duration_days != 0
order by event_id, day
;
The where clause is used when the end_time is midnight (at the beginning of an otherwise "new" day); in that case, presumably, you don't want to include that "new day" in the output, with a duration of 0 minutes.
In the lateral view, level = 1 corresponds to the first date in the interval, while connect_by_isleaf = 1 is for the last date in the interval. A special calculation is made when the end_time and start_time are on the same date. The query computes the difference in days first, then converts to minutes. Note that date calculations aren't 100% precise; I used round so I don't get results like 33.9999999999938020 minutes. If the inputs are in hh24:mi, we know beforehand that the answer (in minutes) should be an integer, so round seems fine there.