PHP無法修改數(shù)據(jù)庫數(shù)據(jù)

卡在ERROR報(bào)錯(cuò)一整天了，求大佬們幫幫忙
核心報(bào)錯(cuò)如圖所示：

完整代碼在此：

<?php
header('Content-Type:textml;charset=utf-8');
$username='游客';
//獲取用戶輸入的賬號(hào)和密碼并連接數(shù)據(jù)庫
$account=$_POST['account'];
$password=$_POST['password'];
$db=new mysqli('localhost','root','12345678','newsmanage');
//查詢數(shù)據(jù)庫是否已經(jīng)有相同賬號(hào)
$query1=$db->prepare("SELECT account FROM user");
$query1->bind_result($theaccount);
$query1->execute();
while($query1->fetch()) {
    if ($account == $theaccount) {
        echo '<script>alert("該賬號(hào)已被注冊(cè)！");location.href="register.html"</script>';
        exit();
    }
}
//將用戶輸入的賬號(hào)和密碼寫入數(shù)據(jù)庫
$add=$db->prepare("INSERT INTO user VALUES (null,'general',null,?,?)");
$add->bind_param('ss',$account, $password);
$add->execute();
//數(shù)據(jù)庫對(duì)添加的新用戶自動(dòng)生成唯一ID，查尋此ID并賦值變量
$query2=$db->prepare("SELECT userid FROM user WHERE account='$account'");
$query2->bind_result($userid);
$query2->execute();
$query2->fetch();
//用username變量修改數(shù)據(jù)表中的數(shù)據(jù)
$edit=$db->prepare("UPDATE user SET username=? WHERE account=?");
$edit->bind_param('ss',$username,$account);
$edit->execute();
//報(bào)錯(cuò)提示：Call to a member function bind_param() on boolean in
echo '<script>alert("恭喜您，注冊(cè)成功！");location.href="../login/login.html"</script>';