<?php
class Db
{
  private $res;
  function __construct($sql)
  {
    $querystr = strtolower(trim(substr($sql,0,6)));
    //如果是select，就連接slave服務(wù)器
    if($querystr == 'select')
    {
      $res=$this->slave_select($sql);
      $this->res=$res;
    }
    //如果不是select，就連接master服務(wù)器
    else
    {
      $res=$this->master_change($sql);
      $this->res=$res;
    }
  }

  /**
   * slave從庫(kù)返回sql查詢(xún)結(jié)果
   * @param $sql
   * @return array
   */
  private function slave_select($sql){
    //該處只是隨機(jī)獲取slave節(jié)點(diǎn)的ip，當(dāng)然，還可以采用其他算法獲取slave_ip
    $slave_server=$this->get_slave_ip();
    $dsn="mysql:host=$slave_server;dbname=test";
    $user='root';
    $pass='123456';
    $dbh=new PDO($dsn, $user, $pass);
    return $dbh->query($sql)->fetchAll(PDO::FETCH_ASSOC);
  }

  /**master主庫(kù)返回sql執(zhí)行結(jié)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);
  }

  /**
   * 隨機(jī)獲取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];
  }

  /**       
   * 獲取結(jié)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());