Adapter \Typecho\Db\Adapter\Pdo\Mysql is not available

Typecho\Db\Exception: Adapter \Typecho\Db\Adapter\Pdo\Mysql is not available in C:\xampp\htdocs\var\Typecho\Db.php:115 Stack trace: #0 C:\xampp\htdocs\config.inc.php(21): Typecho\Db->__construct('\\Typecho\\Db\\Ada...', 'typecho_') #1 C:\xampp\htdocs\index.php(11): include_once('C:\\xampp\\htdocs...') #2 {main}