I want to find the difference(duration) between logon and logoff time?

Question

i want to find the difference(duration) between logon and logoff time of below table?
can any one tell the query to find using self join?
USR     LOGON_TIME     LOGOFF_TIME
HR     31-AUG-04 03.04.04.000000 AM     -
HR     - 31-AUG-04 03.04.14.000000 AM
Edited by: 794244 on Nov 1, 2010 10:47 PM

Answer 1

No selfjoin, just analytical functions.
CREATE TABLe log_time
(username varchar(20),
LOGON_TIME timestamp,
LOGOFF_TIME timestamp);
insert into  log_time (username,LOGON_TIME,LOGOFF_TIME) values ('HR',sysdate,null);
insert into  log_time (username,LOGON_TIME,LOGOFF_TIME) values ('HR',null,sysdate+1/38);
insert into  log_time (username,LOGON_TIME,LOGOFF_TIME) values ('HR',sysdate+2,null);
insert into  log_time (username,LOGON_TIME,LOGOFF_TIME) values ('HR',null,sysdate+2+14/20);
commit;
SELECT username,logon_time,logoff_time, my_logoff_time, my_logoff_time -logon_time,
       time_to_sort
FROM (
        SELECT username,logon_time, logoff_time,
               LEAD(logoff_time,1,logon_time) OVER (PARTITION BY username ORDER BY time_to_sort) my_logoff_time,
               time_to_sort
        FROM (SELECT username,logon_time,logoff_time,NVL(logon_time,logoff_time) time_to_sort
              FROM log_time)
where LOGON_TIME is not null     
ORDER BY  time_to_sort; 
USERNAME     LOGON_TIME     LOGOFF_TIME     MY_LOGOFF_TIME     MY_LOGOFF_TIME-LOGON_TIME     TIME_TO_SORT
HR     02.11.10 11:34:56.000000000          02.11.10 12:12:50.000000000     0 0:37:54.0     02.11.10 11:34:56.000000000
HR     04.11.10 11:34:56.000000000          05.11.10 04:22:56.000000000     0 16:48:0.0     04.11.10 11:34:56.000000000But, if that code which fills that table should better UPDATE than INSERT. You can cover much more issues. (e.g the DB crashes and you get 2 logon but no logoff in a sequence and.....)
-- andy