如果错误，我无法弄明白

Question

我有以下代码，以便在将记录写入数据库之前，它会检查是否存在已存在的用户名.....

$duplicate=mysql_query("SELECT username FROM user WHERE username='" . $username . "'"); 


if ($duplicate <> $username) {
        $insertquery = mysql_query("insert into user                (username, password, lastlogin, address1, address2,             address3, email) values ('$userid', '$password', now            (),'$address1','$address2','$address3','$email')");
    //$msg = "Successfully Registered!";
    $msg = mysql_fetch_assoc($username);
  } else {

    $pass_err = "This Username Is Already In Use!";
    $msg = "This Username Is Already In Use!";
    $userid="";
    $err_flag="False";
    $dupe="";
    $numrecords=0;
}
}

我错过了什么？它总是说它已经存在，当我知道它不存在时......

Answer 1

缺少提取语句

$duplicate=mysql_query("SELECT username FROM user WHERE username='" . $username . "'"); 
$row=mysql_fetch_array($duplicate);

if ($row['username'] == $username) {
    // your code
}

Answer 2

在mysql查询之后，您需要获取结果

$duplicate = mysql_result($duplicate);