Substrating a value from its previous value

Question

suppose i have the data in a column like
col
200
230
250
290
300
then the output should show
col output
200 Null
230 30
250 20
290 40
300 10
can anybody help?

Answer 1

Here is the sample ->
satyaki>
satyaki>select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Prod
PL/SQL Release 10.2.0.3.0 - Production
CORE    10.2.0.3.0      Production
TNS for 32-bit Windows: Version 10.2.0.3.0 - Production
NLSRTL Version 10.2.0.3.0 - Production
Elapsed: 00:00:00.75
satyaki>
satyaki>with t
  2  as
  3    (
  4     select 200 cola from dual
  5     union all
  6     select 230 from dual
  7     union all
  8     select 250 from dual
  9     union all
10     select 290 from dual
11     union all
12     select 300 from dual
13    )
14  select cola, (cola - prev_cola) output
15  from (
16         select cola,
17                lag(cola,1,null) over(order by cola) prev_cola
18         from t
19       );
      COLA     OUTPUT
       200
       230         30
       250         20
       290         40
       300         10
Elapsed: 00:00:00.01
satyaki>
satyaki>Regards.
Satyaki De.