mysqli does not execute Select statement - php

Question

I have the code bellow. When I use this code without the WHERE clause, all the users from the table are displayed, as expected. But when the WHERE clause is used, nothing is displayed.
What could be the cause and how can I fix it?
Thank you!
function requestUser($user) {
$DBHost = "localhost";
$DBUser = "dbUser";
$DBPass = "dbPass";
$DBName = "dbName";
$db = new mysqli($DBHost, $DBUser, $DBPass, $DBName);
if ($db -> connect_errno > 0) {
$lbOK = false;
}
else {
$lbOK = $db -> set_charset('utf8');
}
if ($lbOK) {
$id = NULL;
$user_name = NULL;
$user = htmlentities($user, ENT_QUOTES);
$lcSQL = "SELECT `user_name` FROM `users` WHERE user_name=?";
$stmt = $db -> prepare($lcSQL);
$ok = $stmt -> bind_param('s', $user);
$ok = $stmt -> execute();
$ok = $stmt -> bind_result($user_name);
while ($row = $stmt -> fetch()){
echo $user_name;
}
$stmt->close();
}
}

Answer 1

There are many major faults with your code, some of them can be responsible for the problem, and some not. But nevertheless, they all have to be corrected
Never connect co database inside of an application function. Connect somewhere in the bootstrap file, once, and use that single connection throughout all the application.
Do not use htmlentities with whatever database interactions. It may easily spoil the data
Always check for the the errors
Do not use mysqli, it is unusable. Use PDO instead.
$dsn = "mysql:host=DBHost;dbname=DBName;charset=utf8";
$opt = array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
);
$pdo = new PDO($dsn,$DBUser, $DBPass, $opt);
function requestUser($user) {
global $db;
$sql = "SELECT `user_name` FROM `users` WHERE user_name=?";
$stmt = $db->prepare($sql);
$stmt->execute(array($user));
return $stmt->fetchColumn();
}
echo requestUser($user);
if it still doesn't work, verify it this way
$sql = "SELECT `user_name` FROM `users` WHERE user_name='$user'";
var_dump($sql);
and then try to run in console/phpmyadmin to find out what's wrong with your data/value