getting mysql_numrows(): supplied argument is not a valid MySQL result resource - php

Question

I am trying to create a simple process that checks if a username is taken already during the login process.
I have a simple php script that querys the database and then i check to see if there are any results and echos a response to the user
the full error that i get is:
mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home1/tbronson/public_html/sandbox/uname_check.php on line 9
The entire php script is:
<?php
$user = "(removed for security)";
$pass = "(removed for security)";
$db = "budgetbidders_users";
$con = mysqli_connect($host,$user,$pass,$db);
$uname = strip_tags( trim( $_POST['uname'] ) );
$result = mysqli_query($con,"SELECT * FROM `users` WHERE uname = '" .$uname . '");
$numrows = mysql_num_rows($result); //line 9
if ($numrows > 0) {
$end_result = "Username already taken";
}
else {
$end_result = "";
}
echo $end_result;
?>
I have searched for hours and tried multiple variations, this seems to be the closest to correct that i can find, thank you for your help!

Answer 1

There were a few errors in your code.
The following line has a missing double-quote before the single quote for $uname:
$result = mysqli_query($con,"SELECT * FROM `users`
WHERE uname = '" .$uname . '");
^
However it would be better to use prepared statements or PDO along or you can use:
WHERE uname = '$uname' // instead
Plus, you're mixing the deprecated mysql_* function with the mysqli_* functions.
mysqli_query and mysqli_num_rows() where mysql_num_rows() needs to be changed to mysqli_num_rows
I also suggest you change:
$uname = strip_tags( trim( $_POST['uname'] ) );
to:
$uname = mysqli_real_escape_string($con, $_POST['uname']);
And:
WHERE uname = '" .$uname . "'
to:
WHERE uname = '$uname'
You can make any modifications you wish, both will work. Do read this article on SO on how to prevent SQL injection.
Give this a try now:
<?php
$user = "(removed for security)";
$pass = "(removed for security)";
$db = "budgetbidders_users";
$con = mysqli_connect($host,$user,$pass,$db);
// the line below is better to use
$uname = mysqli_real_escape_string($con, $_POST['uname']);
// this is your original line of code which will work also
// $uname = strip_tags( trim( $_POST['uname'] ) );
$result = mysqli_query($con,"SELECT * FROM `users` WHERE uname = '" .$uname . "' ");
$numrows = mysqli_num_rows($result); //line 9
if ($numrows > 0) {
$end_result = "Username already taken";
} else {
$end_result = "";
}
echo $end_result;
?>

Answer 2

That is beacase u are using mysql_ instead of mysqli_
try this
$numrows = mysqli_num_rows($result):

Answer 3

You cannot mix mysql_* and mysqli_* syntax.
In your case you need:
$numrows = mysqli_num_rows($result);
And you have a syntax error on the line before it (a missing quote).