public function getPrimaryKey($table)
    {
        if (! $table) {
            return '';
        }

        $sql = "SELECT cols.column_name
            FROM all_constraints cons, all_cons_columns cols
            WHERE upper(cols.table_name) = upper('{$table}')
                AND cons.constraint_type = 'P'
                AND cons.constraint_name = cols.constraint_name
                AND cons.owner = cols.owner
                AND cols.position = 1
                AND cons.owner = (select user from dual)
            ORDER BY cols.table_name, cols.position";
        $data = $this->connection->selectOne($sql);

        if ($data) {
            return $data->column_name;
        }

        return '';
    }