code: public void addUniqueConstraint(UniqueConstraint uc) {
  		if (uc.isPrimaryKey()) {
  			if (pk != null)
  				throw new IllegalArgumentException("Duplicate PK " + pk + " " + uc);
  			pk = uc;
  		}
  		else {
  			if (pk != null)
  				if (uc.getAttributes().equals(pk.getAttributes()))
  					// ignore the unique index created for the primary key
  					return;
  		}
  		ucs.add(uc);
  	}
docs: adds a unique constraint (a primary key or a unique constraint proper)
  
  @param uc