连接数据库失败: SQLSTATE[HY000] [2002] 由于目标计算机积极拒绝，无法连接。<br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function exec() on null in C:\xampp\htdocs\Mass\admin\install.php:48
Stack trace:
#0 {main}
  thrown in <b>C:\xampp\htdocs\Mass\admin\install.php</b> on line <b>48</b><br />