protected function _foreignKeySQL($enableDisable)
    {
        $startQuote = $this->_startQuote;
        $endQuote = $this->_endQuote;
        if (!empty($this->_config['schema'])) {
            $schemaName = strtoupper($this->_config['schema']);
            $fromWhere = "from sys.all_constraints
                where owner = '{$schemaName}' and constraint_type = 'R'";
        } else {
            $fromWhere = "from sys.user_constraints
                where constraint_type = 'R'";
        }
        return "declare
            cursor c is select owner, table_name, constraint_name
                {$fromWhere};
            begin
                for r in c loop
                    execute immediate 'alter table " .
                    "{$startQuote}' || r.owner || '{$endQuote}." .
                    "{$startQuote}' || r.table_name || '{$endQuote} " .
                    "{$enableDisable} constraint " .
                    "{$startQuote}' || r.constraint_name || '{$endQuote}';
                end loop;
            end;";
    }