>
> ie i want 1 to 1 mapping between group_id and userid so that , there
> shud not be a single group_id having more that one kind of userid.
>
> can it be done with some sort of UNIQUE INDEX?
If you want multiple groups but the user should always be the same
1 1 ok
1 1 ok
2 1 ok
3 2 ok
3 3 bad
Perhaps you should normalise a bit further with a separate group_user
table - you could restrict that to being unique on group then.
- Richard Huxton