Check that no existing record already has this combination of values across all of the given
fields - a single field for a normal unique/primary key, or several for a composite one.
references and checkKeys are parallel arrays: references[i]'s value must equal checkKeys[i].
Check that no existing record already has this combination of values across all of the given fields - a single field for a normal unique/primary key, or several for a composite one. references and checkKeys are parallel arrays: references[i]'s value must equal checkKeys[i].