Figure 2: Row number, sorted by unique combination of columns (orderdate, orderid)
rownum orderdate orderid empid custid qty
1 2003-08-02 30001 3 B 10
2 2003-12-24 10001 1 C 10
3 2003-12-24 10005 1 A 30
4 2004-01-09 40001 4 A 40
5 2004-01-18 10006 1 C 10
6 2004-02-12 20001 2 B 20
7 2004-02-12 40005 4 A 10
8 2004-02-16 20002 2 C 20
9 2004-04-18 30003 3 B 15
10 2004-04-18 30004 3 B 20
11 2004-09-07 30007 3 C 30