Please help its urgent

[aditya12c]

i have a data which will be updated daily in database.. my crystal report will show all that data..

Now here is da query on which i need help..



Take an example i have values shown on report.. eg

100

300

500

900

1000

.........

note above values will keep on increasing every day..

OUTPUT should be

300 - 100 = 200

500 - 300= 200 .........

so its like i want difference by subracting second value (D2) minus (D1) and then (D3) minus (D2) and so on till it encounters last row.

ACTUAL VALUES .......... how can i get
FROM DB ......... DIFFERENCE OUTPUT ........ OUTPUT

100 .................... ( 300 minus 100 ) ......... 200

300 .................... ( 500 minus 300 ) ......... 200

500 .................... ( 900 minus 500 ) ......... 400

900 .................... ( 1000 minus 900 ) ......... 100

1000 .................... last row will be blank as below this der is no row


i hope u ppl get ma query and plz help me.. its urgent

[TripperDay]

Next({field}) - {field}