Dear Experts

Table1 has Three fields as

code n(2)
cmon c(3)
nyear n(4)

and data in fields is as

code--cmon--year
10----Oct---2006
3-----Mar---2007
11----Nov---2006
7-----Jul---2006
6-----Jun---2007
12----Dec---2006
2-----Feb---2007
8-----Aug---2006
5-----May---2007
1-----Jan---2007
9-----sep---2006
4-----Apr---2007

Now I Want to sort data as

7-----Jul---2006
8-----Aug---2006
9-----sep---2006
10----Oct---2006
11----Nov---2006
12----Dec---2006
1-----Jan---2007
2-----Feb---2007
3-----Mar---2007
4-----Apr---2007
5-----May---2007
6-----Jun---2007

Months are from 7 to 12 and then 1 to 6

What index expression should I apply

Please help