sql unique constraint on a 2 columns combination

Question

How can you create a unique constraint on a combination of two values in two columns.

meaning

column1  column2 
   2        1 

lo

Answer 1

Looking at the documentation, found this for the ORACLE SGBD :

CREATE TABLE b(
 b1 INT, 
 b2 INT, 
 CONSTRAINT bu1 UNIQUE (b1, b2) 
                USING INDEX (create unique index bi on b(b1, b2)),
 CONSTRAINT bu2 UNIQUE (b2, b1) USING INDEX bi);

Chapter "Specifying the Index Associated with a Constraint" on the page ORACLE documentation.

Hop this help.