How does one get the time difference between two date columns?

Oracle allows two date values to be subtracted from each other returning a numeric value indicating the number of days between the two dates (may be a fraction). This example will show how to relate it back to a time value.

Let's investigate some solutions. Test data:

SQL> CREATE TABLE dates (date1 DATE, date2 DATE);
Table created.
SQL>
SQL> INSERT INTO dates VALUES (SYSDATE, SYSDATE-1);
1 row created.
SQL> INSERT INTO dates VALUES (SYSDATE, SYSDATE-1/24);
1 row created.
SQL> INSERT INTO dates VALUES (SYSDATE, SYSDATE-1/60/24);
1 row created.
SQL> SELECT (date1 - date2) FROM dates;
DATE1-DATE2
-----------
        1
.041666667
.000694444

Solution 1

SQL> SELECT floor(((date1-date2)*24*60*60)/3600)
2         || ' HOURS ' ||
3         floor((((date1-date2)*24*60*60) -
4         floor(((date1-date2)*24*60*60)/3600)*3600)/60)
5         || ' MINUTES ' ||
6         round((((date1-date2)*24*60*60) -
7         floor(((date1-date2)*24*60*60)/3600)*3600 -
8         (floor((((date1-date2)*24*60*60) -
9         floor(((date1-date2)*24*60*60)/3600)*3600)/60)*60) ))
10         || ' SECS ' time_difference
11    FROM dates;
TIME_DIFFERENCE
--------------------------------------------------------------------------------
24 HOURS 0 MINUTES 0 SECS
1 HOURS 0 MINUTES 0 SECS
0 HOURS 1 MINUTES 0 SECS

Solution 2

SQL> SELECT to_number( to_char(to_date('1','J') +
2         (date1 - date2), 'J') - 1)  days,
3         to_char(to_date('00:00:00','HH24:MI:SS') +
4         (date1 - date2), 'HH24:MI:SS') time
5   FROM dates;
    DAYS TIME
---------- --------
       1 00:00:00
       0 01:00:00
       0 00:01:00

Solution 3

SQL> SELECT trunc(date1-date2) days,
2         trunc(sysdate) + (date1 - date2), 'HH24 "Hours" MI "Minutes" SS "Seconds"') time
3   FROM dates;
    DAYS TIME
---------- ------------------------------
       1 00 Hours 00 Minutes 00 Seconds
       0 01 Hours 00 Minutes 00 Seconds
       0 00 Hours 01 Minutes 00 Seconds