Difference between current row and previous row in a table

Question

Hi All,
I am having a problem with the query. Can some of please help me?
I need to get difference between current row and previous row in a table. I have a table, which have data like bellow.
TABLEX
================
Name Date Items
AAA 01-SEP-09 100
BBB 02-SEP-09 101
CCC 03-SEP-09 200
DDD 04-SEP-09 200
EEE 05-SEP-09 400
Now I need to get output like bellow...
Name Date Items Diff-Items
AAA 01-SEP-09 100 0
BBB 02-SEP-09 101 1
CCC 03-SEP-09 200 99
DDD 04-SEP-09 200 0
EEE 05-SEP-09 400 200
Can some one help me to write a query to get above results?
Please let me know if you need more information.
Thanks a lot in advance.
We are using Oracle10G(10.2.0.1.0).
Thanks
Asif

Answer 1

     , nvl (items - lag (items) over (order by dt), 0)like in
SQL> with test as
  2  (
  3  select 'AAA' name, to_date('01-SEP-09', 'dd-MON-rr') dt,  100 items from dual union all
  4  select 'BBB' name, to_date('02-SEP-09', 'dd-MON-rr') dt,  101 items from dual union all
  5  select 'CCC' name, to_date('03-SEP-09', 'dd-MON-rr') dt,  200 items from dual union all
  6  select 'DDD' name, to_date('04-SEP-09', 'dd-MON-rr') dt,  200 items from dual union all
  7  select 'EEE' name, to_date('05-SEP-09', 'dd-MON-rr') dt,  400 items from dual
  8  )
  9  select name
10       , dt
11       , items
12       , nvl (items - lag (items) over (order by dt), 0)
13    from test
14  ;
NAM DT             ITEMS NVL(ITEMS-LAG(ITEMS)OVER(ORDERBYDT),0)
AAA 01-SEP-09        100                                      0
BBB 02-SEP-09        101                                      1
CCC 03-SEP-09        200                                     99
DDD 04-SEP-09        200                                      0
EEE 05-SEP-09        400                                    200
SQL>