def METHOD_NAME(
    table_name: str, schema_name: Optional[str] = None, dblink_name: Optional[str] = None
) -> List[str]:
    """ Grab column names comprising the primary key. """
    sql = """
        select  a.attname as column_name
        from    pg_constraint as c
                cross join unnest(c.conkey) as cols(column_number)
                inner join pg_attribute as a on a.attrelid = c.conrelid and cols.column_number = a.attnum
        where   c.contype = 'p' and c.conrelid = '{table}'::regclass
    """
    rows = _get_whatever(table_name, schema_name, dblink_name, sql, _columns)
    return [r["column_name"] for r in rows]