Oracle 18c

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create table data(
fromTime DATE,
toTime DATE);
insert into data(fromTime, toTime)
values(TO_DATE('2003/05/03 00:00:00', 'yyyy/mm/dd hh24:mi:ss'),
TO_DATE('2003/05/03 02:00:00', 'yyyy/mm/dd hh24:mi:ss'));
1 rows affected

insert into data(fromTime, toTime)
values(TO_DATE('2003/05/03 04:00:00', 'yyyy/mm/dd hh24:mi:ss'),
TO_DATE('2003/05/03 05:00:00', 'yyyy/mm/dd hh24:mi:ss'));
1 rows affected

insert into data(fromTime, toTime)
values(TO_DATE('2003/05/03 15:00:00', 'yyyy/mm/dd hh24:mi:ss'),
TO_DATE('2003/05/03 18:00:00', 'yyyy/mm/dd hh24:mi:ss'));
1 rows affected

SELECT * from data;


FROMTIME
TOTIME


03-MAY-03
03-MAY-03

03-MAY-03
03-MAY-03

03-MAY-03
03-MAY-03


SELECT sum((toTime-fromTime)*24) from data;


SUM((TOTIME-FROMTIME)*24)


6