Database not checking if username is free [closed]

问题

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Closed 6 years ago.

Okay, I have another problem, the code is fixed now:

{ 
   //Check if user already exists 
    $un_check = mysql_query("SELECT Username FROM users WHERE Username = '$un'");  
    if(mysql_num_rows($un_check) >0) {
echo "Username already exists";
}
else{
 // Username Free
}

But the database still allows usernames to be the same. Also, even though it says "username already exists" I still creates the account anyway?

any ideas?

回答1:

try this

$un_check = mysql_query("SELECT Username FROM users WHERE Username = 'POSTVALUE'");  
if(mysql_num_rows($un_check) >0) {
   echo "Username is taken";
}
else{
 // Username Free
}

回答2:

Seems typo change $un to $un_check,

if(mysql_num_rows($un_check) >0) {...

Always have your PHP errors turn on at-least on development environment,

error_reporting(E_ALL);

Note: Please, don't use mysql_* functions in new code. They are no longer maintained and are officially deprecated. See the red box? Learn about prepared statements instead, and use PDO, or MySQLi - this article will help you decide which. If you choose PDO, here is a good tutorial.

回答3:

Change this :-

if(mysql_num_rows($un) >0)

to

if(mysql_num_rows($un_check) >0)

来源：https://stackoverflow.com/questions/17298295/database-not-checking-if-username-is-free