检查数据库中是否已经存在用户名或电子邮件

Question

I want to check if the username of email already exists in the DB when a user signs up to my website. I have the following code which isn't working and i'm not sure why. If anyone could point me in the right direction to validate against already existing info in the DB I would greatly appreciate it! Thanks

$query = mysql_query("
    SELECT * 
    FROM users 
    WHERE username = '". $username ."' 
        OR email = '". $email ."'"
);

if (mysql_num_rows($query) > 0){
    die ('Username or email already in use.');
}

Answer 1

This can be done by changing the username field as a primary key or unique.

Or run the sql

SELECT username FROM table WHERE username='$php_username_var';

Answer 2

Please look at the following code, this is being used on the sign up page of my site, I hope you get your answer.

$sq="SELECT * FROM users WHERE username='$username' and password='$password'";
 $rsult=mysql_query($sq);      $count=mysql_num_rows ($rsult); 
if($count==1){echo "username already in use"; }

else 

{

$sql="INSERT INTO $tbl_name(username, password, sex, place)
VALUES('$username', '$password', '$sex', '$place')"; } 
$result=mysql_query($sql);     if($result)
{header("location:home.php"); }
else 
{ echo "Error, please go back and sign up again! "; }  ?>