Getting the difference between Dates

Frequently we are asked -- how can I find the number of minutes between two dates or what is the amount of elapsed time.  With Oracle Dates, this is pretty trivial, you can get either TOTAL (days, hours, minutes, seconds) between 2 dates simply by subtracting them or with a little mod'ing you can get Days/Hours/Minutes/Seconds between.

For example:

SQL> set serveroutput on
SQL> declare
  2          a       date;
  3          b       date;
  4  begin
  5          a := sysdate;
  6          dbms_lock.sleep(10);    -- sleep about 10 seconds give or take
  7          b := sysdate;
  9          dbms_output.put_line( b-a || ' of a day has elapsed' );
 10          dbms_output.put_line( (b-a)*24 || ' of an hour has elapsed' );
 11          dbms_output.put_line( (b-a)*24*60 || ' of a minute has elapsed' );
 12          dbms_output.put_line( (b-a)*24*60*60 || ' seconds has elapsed' );
 13  end;
 14  /
.000127314814814814814814814814814814814815 of a day has elapsed
.00305555555555555555555555555555555555556 of an hour has elapsed
.1833333333333333333333333333333333333336 of a minute has elapsed
11.00000000000000000000000000000000000002 seconds has elapsed

PL/SQL procedure successfully completed.

To break the diff between 2 dates into days, hours, minutes, sec -- you can use the following:

select to_char( created, 'dd-mon-yyyy hh24:mi:ss' ),
       trunc( sysdate-created ) "Dy",
       trunc( mod( (sysdate-created)*24, 24 ) )  "Hr",
       trunc( mod( (sysdate-created)*24*60, 60 ) )  "Mi",
 trunc( mod( (sysdate-created)*24*60*60, 60 ) ) "Sec",
       to_char( sysdate, 'dd-mon-yyyy hh24:mi:ss' ),
       sysdate-created "Tdy",
       (sysdate-created)*24 "Thr",
       (sysdate-created)*24*60 "Tmi",
       (sysdate-created)*24*60*60 "Tsec"
from all_users
where rownum < 50

Dy gives you number of days between 2 dates (partial days discarded).  Tdy gives you total days including fractions (eg: you'll get 1.5 for 1 and 1/2 days).  Likewise for HR and THR and so on.

Sybase users are used to using datediff in the database and are many times baffled by the lack of a function to do date arithemetic that they assume Oracle cannot do it.  It is really just that date arithmetic is so trivial that a specialized function like datediff is not needed.  Just subtract.  You get the difference in days.  Multiply by 24 -- hours, multiply by 60 minutes, multiply by 60 -- seconds.

If you really want 'datediff' in your database, you can just do something like this:

SQL> create or replace function datediff( p_what in varchar2,
  2                                       p_d1   in date,
  3                                       p_d2   in date ) return number
  4  as
  5      l_result    number;
  6  begin
  7      select (p_d2-p_d1) *
  8             decode( upper(p_what),
  9                     'SS', 24*60*60, 'MI', 24*60, 'HH', 24, NULL )
 10       into l_result from dual;
 11      return l_result;
 12  end;
 13  /

Function created

Now, i just create a view to demonstrate with:

SQL> create or replace view temp_view
  2  as
  3  select to_date('01-JAN-1999 12:02:04', 'dd-mon-yyyy hh24:mi:ss' ) d1,
  4         to_date('15-MAR-1999 01:34:23', 'dd-mon-yyyy hh24:mi:ss' ) d2
  5  from dual
  6  /
View created.

SQL> select datediff( 'ss', d1, d2 ) seconds from temp_view;


SQL> select datediff( 'mi', d1, d2 ) minutes from temp_view;


SQL> select datediff( 'hh', d1, d2 ) hours from temp_view;


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