php--- session

<?php      include "conn.php";     $username = $_GET[userName];    $password = $_GET[userPwd];    /*查询*/    $sql = "SELECT id FROM user where userName='{$username}' and userPwd='{$password}'";    $result = $conn->query($sql);      $row = $result->fetch_assoc();     if($row["id"]){        $_SESSION['username'] = $username;        $_SESSION['userid'] =$row["id"];        echo "welcome,";        echo $username;        echo "<br>";        echo "<br>";        echo "你的id是,";        echo $row["id"];        exit;       }else{          echo "用户名或密码错误";    }    mysqli_close($conn); ?>