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
