Create array from field of db

Create array from field of db

i have a db like this
ID | A | B |
------------
1 | 8 | 9 |
2 | 9 | 11|
3 | 15| 18|
I want to create an array, where the item in the array has the following
formula :
array(
(A(2)-A(1),B(2)-B(1)),
A(3)-A(2),B(3)-B(2))
)
Or, the desired result is like
array(
array(1,2),
array(6,7)
);