composite Unique constraint and null

Hi,

I want to enforce a business rule on two columns such that col1, col2 should be unique. However for a given value of col1 nulls should be allowed in col2. I can not implement that using a simple composite unique constraint.

Eg.

create table foo(id number, name varchar2(10));

insert into foo values(1,1);
insert into foo values(1,1); -- should not be allowed

But following should be allowed

insert into foo values(1,null);
insert into foo values(1,null); -- should be allowed

Any ideas!!

Thanks

Sandeep
Sandeep

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