DEMO, Oracle - rextester

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--Oracle 11g Express Edition
--please drop objects you've created at the end of the script 
--or check for their existance before creating
--'\\' is a delimiter

drop table t1\\

create table t1(
start1   DATE,              
end1     DATE,               
start_day_hours  dec(5,3),   
end_day_hours dec(5,3)
)\\

insert into t1 values(TIMESTAMP '2017-10-02 21:33:00',TIMESTAMP '2017-10-03 00:00:42',2.43,0.71)\\
insert into t1 values(TIMESTAMP '2017-10-03 21:34:00',TIMESTAMP '2017-10-04 00:00:19',2.42,0.32)\\
insert into t1 values(TIMESTAMP '2017-10-04 21:59:00',TIMESTAMP '2017-10-05 00:55:36',2.00,0.92)\\
insert into t1 values(TIMESTAMP '2017-10-16 21:59:00',TIMESTAMP '2017-10-17 00:00:01',2.00,0.01)\\
insert into t1 values(TIMESTAMP '2017-10-18 22:50:00',TIMESTAMP '2017-10-19 00:00:25',1.16,0.42)\\
insert into t1 values(TIMESTAMP '2017-10-19 22:19:00',TIMESTAMP '2017-10-20 00:01:00',1.67,1.01)\\

SELECT date1 AS DAY,
       sum(hours) AS total_hours
FROM
  (SELECT trunc(start1) AS date1,
          start_day_hours AS hours
   FROM t1
   UNION ALL SELECT trunc(end1),
                    end_day_hours
   FROM t1 ) t
GROUP BY date1
ORDER BY date1


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