Oracle SQL time difference in HH:MM:SS - sql

Question

I am trying to get time difference in Oracle database. The time difference for all the rows is okay except for one row. Here is the query
SELECT MAX(REGEXP_SUBSTR (CAST(TO_DATE(call_end, 'YYYY/MM/DD HH24:MI:SS') AS TIMESTAMP) - CAST(TO_DATE(call_start, 'YYYY/MM/DD HH24:MI:SS') AS TIMESTAMP), '\d{2}:\d{2}:\d{2}')) AS call_time
FROM calls
The time difference occurs with the following row:
call_end: '2020-02-20 13:00:20'
call_start: '2020-02-20 12:56:03'
The returned result is '11:55:43' which is wrong. As the correct answer should be '00:04:17'

Answer 1

It looks like your table already stores the call start/end times as dates, and you're doing an implicit conversion from date to string, then converting back to a date. You can see that result if you have HH instead of HH24 in your NLS_DATE_FORMAT setting:
alter session set nls_date_format = 'YYYY-MM-DD HH:MI:SS';
with calls (call_end, call_start) as (
select cast(timestamp '2020-02-20 13:00:20' as date), cast(timestamp '2020-02-20 12:56:03' as date) from dual
)
SELECT MAX(REGEXP_SUBSTR (CAST(TO_DATE(call_end, 'YYYY/MM/DD HH24:MI:SS') AS TIMESTAMP) - CAST(TO_DATE(call_start, 'YYYY/MM/DD HH24:MI:SS') AS TIMESTAMP), '\d{2}:\d{2}:\d{2}')) AS call_time
FROM calls;
CALL_TIME
---------------------------
11:55:43
When you do
TO_DATE(call_end, 'YYYY/MM/DD HH24:MI:SS')
because it's already a date you're really doing:
TO_DATE(TO_CHAR(call_end, <NLS_DATE_FORMAT>), 'YYYY/MM/DD HH24:MI:SS')
so with my setting (and yours must be similar, maybe with slashes instead of dashes) that is:
TO_DATE(TO_CHAR(call_end, 'YYYY-MM-DD HH:MI:SS'), 'YYYY/MM/DD HH24:MI:SS')
and the mismatch between HH and HH24 becomes more obvious. So, you're actually converting the strings 2020-02-20 01:00:20 and 2020-02-20 12:56:03 back to dates, and the time difference between 01:00:20 and 12:56:03 is 11:55:43. Well - actually, it is minus 11 hours:
SELECT CAST(TO_DATE(call_end, 'YYYY/MM/DD HH24:MI:SS') AS TIMESTAMP) - CAST(TO_DATE(call_start, 'YYYY/MM/DD HH24:MI:SS') AS TIMESTAMP)
FROM calls;
CAST(TO_DATE(CALL_E
-------------------
-00 11:55:43.000000
but your regex isn't picking that up.
As they are dates skip that part of the conversion completely, and just cast directly to timestamps if you want intervals to work from:
SELECT MAX(REGEXP_SUBSTR (CAST(call_end AS TIMESTAMP) - CAST(call_start AS TIMESTAMP), '\d{2}:\d{2}:\d{2}')) AS call_time
FROM calls;
CALL_TIME
---------------------------
00:04:17
or use a substring instead of a regex, as #MTO showed.
You could also leave them as dates, get the difference as a fraction of a day, add that back to any nominal date at midnight, and then convert the resulting date to a string:
SELECT TO_CHAR(date '2000-01-01' + MAX(call_end - call_start), 'HH24:MI:SS') AS call_time
FROM calls;
CALL_TIM
--------
00:04:17
This won't work properly for a call that lasts more than 24 hours (used to see that a lot with modem calls, but can still happen); but neither will your interval approach. Both ignore any full days and just show the remainder. There are ways to handle that of course, but you'd need to decide how you want to display it - with separate day count (like interval does anyway), or with the 'hours' number allowed to go above 24... but then you may go above 99 hours...
Your question shows the call end time as 2020-02-20 13:00:20, which suggests that's how your client is displaying it when you query the table. Some clients (I think PL/SQL Developer, but not sure, it's been a while) use their own preferences/settings instead of honouring the session's NLS settings. But that has no effect on how Oracle behaves internally when it has to do implicit conversions.

Answer 2

I'm not sure if you want the result as an interval or timestamp, but this should do what you want:
select t.*, call_end - call_start,
substr(to_char(call_end - call_start, 'HH24:MI:SS'), 12, 8) as str from (select timestamp '2020-02-20 13:00:20.000' as call_end,
timestamp '2020-02-20 12:56:03.000' as call_start
from dual) t
Here is a db<>fiddle.

Answer 3

Assuming your data types are strings (you really should store them as DATE data types), you can use:
SELECT SUBSTR(
MAX(
( TO_DATE( call_end, 'YYYY-MM-DD HH24:MI:SS' )
- TO_DATE( call_start, 'YYYY-MM-DD HH24:MI:SS' )
) DAY(1) TO SECOND
),
4,
8
) AS call_time
FROM calls
If they are already DATE data types then, in the MAX aggregation, just use:
( call_end - call_start ) DAY(1) TO SECOND
So for your data:
CREATE TABLE calls ( call_end, call_start ) AS
SELECT '2020-02-20 13:00:20', '2020-02-20 12:56:03' FROM DUAL
This outputs:
| CALL_TIME |
| :-------- |
| 00:04:17 |
db<>fiddle here

Answer 4

Mr Gyl, You can as well do: db <> fiddle :This solution will also consider when the call has lapsed over days by adding those hours together:
WITH da AS (
SELECT
NUMTODSINTERVAL(TO_DATE('2020-02-20 13:00:20', 'yyyy-mm-dd hh24:mi:ss') - TO_DATE('2020-02-20 12:56:03', 'yyyy-mm-dd hh24:mi:ss'), 'DAY') AS call_diff
FROM
dual ) SELECT
EXTRACT( DAY FROM call_diff )*24 + EXTRACT( HOUR FROM call_diff )|| ':' || EXTRACT( MINUTE FROM call_diff ) || ':' || EXTRACT( SECOND FROM call_diff ) DIFFERENCE
FROM
da
DIFFERENCE|
----------|
0:4:17 |
So you can implement as
WITH da AS (
SELECT
NUMTODSINTERVAL(TO_DATE(call_end, 'yyyy-mm-dd hh24:mi:ss') - TO_DATE(call_start, 'yyyy-mm-dd hh24:mi:ss'), 'DAY') AS call_diff
FROM
calls
) SELECT
EXTRACT( DAY FROM call_diff )*24 + EXTRACT( HOUR FROM call_diff )|| ':' || EXTRACT( MINUTE FROM call_diff ) || ':' || EXTRACT( SECOND FROM call_diff ) TIMESTAMP
FROM
da

Answer 5

Please see below response but this will only work within 24hrs and returns both '00'
WITH sample_lt AS(
SELECT '2020-02-20 12:56:03' START_TIME, '2020-02-20 13:00:20' END_TIME FROM dual
)
SELECT start_time,
end_time,
TO_CHAR (TRUNC (SYSDATE) + (to_date(end_time, 'yyyy-mm-dd HH24:MI:SS') -
to_date(start_time, 'yyyy-mm-dd HH24:MI:SS')
) , 'hh24:mi:ss' ) duration
FROM sample_lt ;