SQL> drop table faq;

Table dropped.

SQL> create table faq
  2  ( col1 number
  3  , col2 date
  4  );

Table created.

SQL> insert into faq values (8, to_date('05-01-2007', 'dd-mm-yyyy'));

1 row created.

SQL> insert into faq values (9, to_date('06-01-2007', 'dd-mm-yyyy'));

1 row created.

SQL> insert into faq values (1, to_date('01-01-2007', 'dd-mm-yyyy'));

1 row created.

SQL> insert into faq values (2, to_date('02-01-2007', 'dd-mm-yyyy'));

1 row created.

SQL> insert into faq values (5, to_date('03-01-2007', 'dd-mm-yyyy'));

1 row created.

SQL> insert into faq values (2, to_date('04-01-2007', 'dd-mm-yyyy'));

1 row created.

SQL> 
SQL> select col1 - lag(col1) over (order by col2)
  2  ,	    col2
  3  from   faq
  4  order  by col2
  5  ;

COL1-LAG(COL1)OVER(ORDERBYCOL2) COL2
------------------------------- ---------
                                01-JAN-07
                              1 02-JAN-07
                              3 03-JAN-07
                             -3 04-JAN-07
                              6 05-JAN-07
                              1 06-JAN-07

6 rows selected.