search SQL for possibly duplicated user names using PHP - php

Question

I want to search my database to see if a user that is registering is using a username that is currently in my database. I have registered the same name about 5 times so it SHOULD return false but it returns true.
<?php
function registerUser($userName, $userPassword) {
$db = new dbinterface();
$db->connect();
// check for duplicate data
$checkduplicates = "SELECT * FROM usersexample WHERE $userName = :userName";
$myresult = mysql_query($checkduplicates);
if(mysql_num_rows($myresult) > 0){
echo $myresult;
return false;
}
?>
My table name is usersexample and the field i am searching is userName.
ANY and ALL help is appreciated!
Using mysql_num_rows in examples i get this warning:
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource.

Answer 1

Use mysql_num_rows() to check the number of rows returned.
Sample:
$myresult = mysql_query($checkduplicates);
$rowcount = mysql_num_rows($myresult);
if($rowcount > 0)
{
// Account name already in use
}

Answer 2

You should try this...
if(mysql_num_rows($myresult) > 0) {
echo $myresult;
return false;
}
It will return false if there is a duplicate username.

Answer 3

$getduplicates = mysql_query("SELECT * FROM table WHERE username = $username");
$duplicates = mysql_num_rows($getduplicates);
if($duplicates){
echo "Uh oh someone already has that username";
}
else {
echo "Everything is allllllll good";
}

Answer 4

Please use prepared statements to avoid sql injection.
As you are using :userName in your SQL it seems you are trying to do this (is your
database class based on PDO by any chance?). The :userName part will be replaced
by your variable $userName when you do the bindValue.
Use count() in the database to count the number of records found,
the database knows best ;-)
$query = $db->prepare("SELECT count(*) AS no_found FROM usersexample WHERE userName = :userName");
$query->bindValue(':userName', $userName, PDO::PARAM_STR);
$query->execute();
$result = $query->fetchObject();
if($result->no_found > 0)
{
return false;
}

Answer 5

Did you try:
$checkduplicates = "SELECT userName FROM usersexample
WHERE LOWER('".$userName."') = LOWER(userName)";
$myresult = mysql_query($checkduplicates)
if (!$myresult) {
die('Invalid query: ' . mysql_error());
} else {
$num_rows = mysql_num_rows($myresult);
if (!$num_rows) {
die('Invalid query: ' . mysql_error());
} else return ($num_rows == 0);
}
Please, sanitize user input to avoid SQL injection.

Answer 6

I don't know if you are doing something fancy I don't understand, but I would build the query like this:
$checkduplicates = "SELECT * FROM `usersexample` WHERE `userName` = '$userName'";
Or this
$checkduplicates = "SELECT * FROM `usersexample` WHERE `userName` = '".$userName."'";