Urgent Query

From: Windsurfer <nsingh49_at_yahoo.com>
Date: 13 Jan 2004 10:41:00 -0800
Message-ID: <14bd0e63.0401131041.5d0a521d@posting.google.com>

Here is my question:

create table x (t varchar2(10), dt date);

data in the table x( Keep in mind, I actual table it has over 3 million rows, so performance is critical )

t                       dt
-------------        ------------
1001                 01/01/2004 10:10:00
1001                 01/01/2004 10:11:00
1001                 01/01/2004 10:12:00
1001                 01/01/2004 10:13:00
1002                 01/01/2004 11:10:00
1002                 01/01/2004 11:11:00
1002                 01/01/2004 11:12:00
1002                 01/01/2004 11:13:00

I need to write a query to tell me for each row when was the last dt/time:
so for 1001 and 1002 i will have one less record:

t                  dt                      previous_dt
------------  -----------------      --------------------
1001          01/01/2004 10:11:00    01/01/2004 10:10:00
1001          01/01/2004 10:12:00    01/01/2004 10:11:00
1001          01/01/2004 10:13:00    01/01/2004 10:12:00
1002          01/01/2004 10:11:00    01/01/2004 10:10:00
1002          01/01/2004 10:12:00    01/01/2004 10:11:00
1002          01/01/2004 10:13:00    01/01/2004 10:12:00

Thanks alot Received on Tue Jan 13 2004 - 12:41:00 CST