public function getMatchingColumns($table1, $which_connection1, $table2, $which_connection2)
    {
        $def1 = $this->tableDefinition($table1, $which_connection1);
        $def2 = $this->tableDefinition($table2, $which_connection2);
        $ret = array_reduce(array_keys($def1),
            function ($carry, $column_name) use ($def2) {
                if (isset($def2[$column_name])) {
                    $carry .= $column_name . ',';
                }
                return $carry;
            },
            ''
        );
                
        if ($ret === '') {
            return false;
        } else {
            return substr($ret, 0, strlen($ret)-1);
        }
    }