pdo 执行sql

<?php
$host     = '127.0.0.1';
$user     = 'root';
$pwd      = '123456';
$dbname   = 'test';

// sql
$sql = "delete from user where id=1;";

try {
    // 连接数据库
    $conn = new PDO('mysql:host=' . $host . ';dbname=' . $dbname . '', $user, $pwd);
    // 设置 PDO 错误模式为异常 
    $conn->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
    $conn->exec('set names "utf8"');
    // 使用 exec() ，因为没有结果返回 
    $affected = $conn->exec($sql);
    if ($affected !== false) {
        echo 1;
        return;
    } else {
        echo 2;
        $conn = null;
        return;
    }
} catch (PDOException $e) {
    // echo $sql . "<br>" . $e->getMessage();
    echo 0;
    $conn = null;
    return;
}