public function getPrimaryKey($tableName)
    {
        $indexes = $this->query("EXEC sp_helpindex '$tableName';");
        $indexName = '';
        foreach ($indexes as $index) {
            if ($index['index_keys'] == 'ID') {
                $indexName = $index['index_name'];
                break;
            }
        }

        return $indexName;
    }