create table test_bf_af ( e_id number, e_amt number(17,2));

INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
1, 16880); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
2, 2500); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
3, 4100); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
4, 2500); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
5, 18480); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
6, 2500); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
7, 5600); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
8, 2500); 
INSERT INTO TEST_BF_AF ( E_ID, E_AMT ) VALUES ( 
9, 7650); 
COMMIT;

I need to list the above data as 

e_id	       e_amt		e_amt
	       before		after

1	       0		16880
2	       16880		2500
3	       2500		4100
4	       4100		2500
5	       2500		18480
6	       18480		2500
7	       2500		5600
8	       5600		2500
9	       2500		7650

select 
  e_id,
  nvl(lag(e_amt) over (order by e_id), 0) amt_before,
  e_amt amt_after
from test_bf_af 

select 
  e_id,
  lag(e_amt, 1, 0) over (order by e_id) amt_before,
  e_amt amt_after

lag(e_amt,1,0) over (order by e_id) amt_before,