I'm thinking of ADD CONSTRAINT to my db table as per example from http://www.w3schools.com/sql/sql_unique.asp
ALTER TABLE Persons ADD CONSTRAINT uc_PersonID UNIQUE (P_Id,LastName)
Instead of a unique constraint, just add a unique index:
CREATE UNIQUE INDEX unq_persons_pid_lastname ON PERSONS(P_Id, LastName);
It is curious that you would have a table called
Persons and that
P_Id would not already be unique in the table (by being a primary key).