SQL & PL/SQL

I want to merge consecutive rows of a table. i.e. if my table has 4 rows of data then my ouput of query will have only 3 rows because
rows 1 and 2 are merged to first row of result
rows 2 and 3 are merged to second row of result
rows 3 and 4 are merged to third row of result

For example if my table is
____
A | B
-------
1 | 4
9 | 7
3 | 2
7 | 9

then output of query should be
____________
A | B |A1| B1
---------------------
1 | 4 | 9 | 7
9 | 7 | 3 | 2
3 | 2 | 7 | 9

How can i write a query to achieve this?