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