php中唯一的用户ID代码不起作用

Question

Recently i was searching for unique username registration using php.. I came across a piece of code which i am displaying below:

<?php 
$fname=trim($_POST['fname']);
$lname=trim($_POST['lname']);
$email=trim($_POST['email']);
$usn=trim($_POST['usn']);
$dept=trim($_POST['dept']);
$pass=trim($_POST['pass']);
$tel=trim($_POST['tel']);

$dbh = mysql_connect('localhost', 'root','') or die("<h3 style=\"color:red;\" align=\"center\">SERVER ERROR</h3>");
mysql_select_db('fy') or die("<h3 style=\"color:red;\" align=\"center\">SERVER ERROR</h3>");

$error= mysql_query("SELECT * FROM stud WHERE email='$email' OR usn='$usn' OR tel='$tel'") or die (mysql_error()); 

if (mysql_num_rows($error) > 0);
{
    die ("Sorry! Either email, usn or tel already exists!");
}

$query="INSERT INTO stud (fname, lname, email, tel, usn, dept, pass) VALUES ('$fname', '$lname', '$email', '$tel', '$usn', '$dept', '$pass')";
mysql_query($query);
$query="INSERT INTO log VALUES ('$usn','$pass',0,0)";
mysql_query($query);
print("REGISTERED");



 ?>
 <a href="login.php">LOGIN</a><br />

At this moment my database is completely empty. I've just created the database stud with the desired columns. Now the problem is when i try to register using my registration page, it gives me the error i specified in die that is

"Sorry! Either email, usn or tel already exists!"

How is this possible if there are no values in the database. In the registration form I've given

action="register.php" 

as a processing file. Also I've tried with mysql_fetch_assoc(), but i get the same error. Any help is appreciated. Thank you .

Answer 1

Your first problem is that, as John Conde states, your code is vulnerable to SQL injection attacks.

Your second problem, and to answer your question, is probably because you have this:

if (mysql_num_rows($error) > 0);

instead of this:

if (mysql_num_rows($error) > 0)