How to add varchar which is in time format

Question

Hello Team,
can you please help me for the below request?
I have two columns (start and End) which is in varchar type and value is in time format as below. now I wanted to do some addition/subtraction based on condition. while adding or subtracting, it should be considered as time. Thanks in advance.
if start>end then start-End
else end-start
end if
  start                End
23:20:03            00:20:01 
23:37:15            00:37:13 
23:20:26            00:00:02 
23:47:06            00:10:26
00:13:23            00:07:31 
01:23:02            00:52:25

Answer 1

with
times as
(select '23:20:03' start_time,'00:20:01' end_time from dual union all
select '23:37:15','00:37:13' from dual union all
select '23:20:26','00:00:02' from dual union all
select '23:47:06','00:10:26' from dual union all
select '00:13:23','00:07:31' from dual union all
select '01:23:02','00:52:25' from dual
select start_time,end_time,
       to_char(trunc(sysdate) + case when to_date(start_time,'hh24:mi:ss') >= to_date(end_time,'hh24:mi:ss')
                                     then to_date(start_time,'hh24:mi:ss') - to_date(end_time,'hh24:mi:ss')
                                     else to_date(end_time,'hh24:mi:ss') - to_date(start_time,'hh24:mi:ss')
                                end,
               'hh24:mi:ss'
              ) diff      
  from times
START_TIME
END_TIME
DIFF
23:20:03
00:20:01
23:00:02
23:37:15
00:37:13
23:00:02
23:20:26
00:00:02
23:20:24
23:47:06
00:10:26
23:36:40
00:13:23
00:07:31
00:05:52
01:23:02
00:52:25
00:30:37
Regards
Etbin
Oops! Should have looked before posting.