INSERT Row 1: A,A,A  <== OK! Value set unique
INSERT Row 2: A,D,A  <== OK! Value set unique
INSERT Row 3: D,T,G  <== OK! Value set unique
INSERT Row 4: D,A,A  <== OK! Value set unique
INSERT Row 5: A,D,A  <== COLLISION with Row 2! Set not unique; skip INSERT