Composit primary key (reverse)

Question

Hi,
I have created a table with composite primary key
eg:-
create table demo(one NUMBER,two NUMBER,primary key pk_composite (one,two);
insert into demo values(1,2);
1 row inserted
insert into demo values(1,2);
ORA-00001: unique constraint (username.PK_composite) violated
its ok...........................
I know composite primary wont work reverse (i.e)
select * from demo;
one | two
1 | 2
insert into demo values(2,1);
1 row inserted
select * from demo;
one | two
1 | 2
2 | 1
I need the reverse to be done is there any possible solution to make it? (i.e)
insert into demo values(2,1); -- this should not be allowed
please help me... thanks in advance...

Answer 1

A quick way to accomplish this is to create a function-based unique index like this:
create unique index demo_i1 on demo
(least(one,two)
,greatest(one,two));