How to calculate the difference of HH:MM:SS between two dates in oracle sql? - oracle

Question

I have a table abc as:
-- start_time |end_time | total_time_taken
-- 27.05.2020 00:52:48 |27.05.2020 02:08:33 |
I want to set the value of total_time_taken as the difference of end_time-start_time. in the format "HH:MM:SS".I searched the similar topic but didnot find the exact answer.
My expected output is like : 01:44:12 (HH:MM:SS)
So,i tried :
SELECT To_Char(end_time,'HH24:MM:SS'),To_Char(start_time,'HH24:MM:SS'),
To_Char(end_time,'HH24:MM:SS')-To_Char(start_time,'HH24:MM:SS') FROM abc;
The datatypes of start_time,end_time,total_time_taken is DATE.Please help me to find the solution.

Answer 1

If you cast those dates as timestamps, you can easily subtract them and see relatively nice result:
SQL> with test (st, et) as
2 (select to_date('27.05.2020 00:52:48', 'dd.mm.yyyy hh24:mi:ss'),
3 to_date('27.05.2020 02:08:33', 'dd.mm.yyyy hh24:mi:ss')
4 from dual
5 )
6 select cast(et as timestamp) - cast(st as timestamp) diff
7 from test;
DIFF
--------------------------------------------------------------------------
+000000000 01:15:45.000000
SQL>
If you want to format it as you wanted (note that mm format mask is for months; mi is for minutes), then you could do some extracting - again from timestamp (won't work for date):
SQL> with test (st, et) as
2 (select to_date('27.05.2020 00:52:48', 'dd.mm.yyyy hh24:mi:ss'),
3 to_date('27.05.2020 02:08:33', 'dd.mm.yyyy hh24:mi:ss')
4 from dual
5 ),
6 diff as
7 (select cast(et as timestamp) - cast(st as timestamp) diff
8 from test
9 )
10 select extract(hour from diff) ||':'||
11 extract(minute from diff) ||':'||
12 extract(second from diff) diff
13 from diff;
DIFF
-------------------------------------------------------------------------
1:15:45
SQL>
You can further make it pretty (e.g. two digits for hours, using LPAD function). Or, you can even write your own function which will actually work on difference of DATE datatype values, do some calculations (using trunc function, subtractions, whatnot), but the above looks pretty elegant if compared to a home-made function.

Answer 2

The answer by Littlefoot is perfectly fine. This answer is just to show there is more than one way to get the result.
First, we can subtract one date from another and get the difference in days, then convert that difference to an interval.
with test (st, et) as
(select to_date('27.05.2020 00:52:48', 'dd.mm.yyyy hh24:mi:ss'),
to_date('27.05.2020 02:08:33', 'dd.mm.yyyy hh24:mi:ss')
from dual
)
select numtodsinterval(et-st, 'day') diff
from test;
Then, since we can't control interval formatting directly, we can add DIFF to an arbitrary date and then use built-in date formatting.
with test (st, et) as
(select to_date('27.05.2020 00:52:48', 'dd.mm.yyyy hh24:mi:ss'),
to_date('27.05.2020 02:08:33', 'dd.mm.yyyy hh24:mi:ss')
from dual
)
select to_char(date '1-1-1' + numtodsinterval(et-st, 'day'), 'hh24:mi:ss') diff
from test;
DIFF
--------
01:15:45