def METHOD_NAME(table, columns):
    """
    Returns the string name of the unique constraint which applies to the given 
    columns, or None if no matching constraint exists.
    """
    unique_info = None
    for info in sa.inspect(op.get_bind()).get_unique_constraints(table):
        if info['column_names'] == columns:
            unique_info = info
            break
    if unique_info:
        return unique_info['name']
    else:
        return None