myth????
here is the code..
SQL> select * from test;

A B
---------- ----------
3 200
2 300
8 100
5 400
1 300
4 500
8 200
5 300
4 600
2 300
3 500
2 100
7 300

13 rows selected.

SQL> select a,sum(b) from test
2 group by a;

A SUM(B)
---------- ----------
1 300
2 700
3 700
4 1100
5 700
7 300
8 300

7 rows selected.