Serial Number within a group

hi ... has anyone ever implemented a scheme to generate serial numbers that stays within a group? I know that Informix supports serial number that is table wide. However I require something like the following: Table A ------- Col1 Col2 --- ---- 1 1 1 2 1 3 1 4 2 1 2 2 3 1 3 2 etc. Col1 is the group while the numbers in Col2 is serial within its group. Would be grateful for any contributions. /// Koh Nai Pin /// Computer Division 5 /// System & Computer Division /// Singapore