<"mysql:host=$slave_server;dbname=test";
    $user='root';
    $pass='123456';
    $dbh=new PDO($dsn, $user, $pass);
    return $dbh->query($sql)->fetchAll(PDO::FETCH_ASSOC);
  }

  /**master主库返回sql执行结果
   * @param $sql
   * @return int
   */
  private function master_change($sql){
    $master_server='192.168.33.22';
    $dsn="mysql:host=$master_server;dbname=test";
    $user='root';
    $pass='123456';
    $dbh=new PDO($dsn, $user, $pass);
    return $dbh->exec($sql);
  }

  /**
   * 随机获取slave-ip
   * @return mixed
   */
  private function get_slave_ip(){
    $slave_ips=['192.168.33.33','192.168.33.44'];
    $count=count($slave_ips)-1;
    $random_key=mt_rand(0,$count);
    return $slave_ips[$random_key];
  }

  /**       
   * 获取结果
   * @return int
   */
  public function get_res(){
    return $this->res;
  }
}

$sql1 = "select * from t1";
$sql2 = "insert into t1 (name) values ('haha')";
$sql3 = "delete from t1 where id=1";
$sql4 = "update t1 set name='Jerry' where id=2";

$db = new Db($sql1);
//$db = new Db($sql2);
//$db = new Db($sql3);
//$db = new Db($sql4);

var_dump($db->get_res());