php 导出mysql

<?php
$host="localhost";
$user="root";
$password="root";
$dbname="lol";
$db=new PDO("mysql:host=$host;dbname=$dbname", "$user", "$password");
$db->query("set names utf8");

$mysql= "set names utf8;";

$db->query("$mysql");
$res=$db->query("show tables");


while($t=$res->fetch()){
    $table=$t[0];
    $q2=$db->query("show create table `$table`");
    $sql=$q2->fetch();
    $mysql.=$sql["Create Table"].";
";

    $q3=$db->query("select * from `$table`");
    while($data=$q3->fetch(PDO::FETCH_ASSOC)){
        $keys=array_keys($data);
        $keys=array_map("addslashes",$keys);
        $keys=join("`,`",$keys);
        $keys="`".$keys."`";
        $vals=array_values($data);

        $vals=array_map("addslashes",$vals);

        $vals=join("","",$vals);
        $vals=""".$vals.""";
        $mysql.="insert into `$table`($keys) values($vals);
";
    }
    $mysql.="
";
}
$filename=$dbname.date("Ymj").".sql";
$fp = fopen($filename,"w");
fputs($fp,$mysql);
fclose($fp);
echo "数据备份成功,生成备份文件".$filename;