Why not create 3 queries..
The first displays only sub1 and that too only if its value is higher than sub 2 and 3 else is blank...
The second displays only sub2 and that too only if its value is higher than sub1 and 3 else is blank...
The third displays only sub3 and that too only if its value is higher than sub 1 and 2 else is blank...
Finally
Create a third query which combines the data from all three queries and thus displays only the highest value,....
It's pain staking and may create other problems but atleast u don't have to change the table structure...