MySQL and PHP gives me null var - php

Question

I make a random quote app, in which by pressing a button, i can load one random phrase. I created for this a MySQL database, and two php code.
I upload my two code in a web hosting, and the app is running!
But sometime it gives me "null" instead of the phrase. I don't know why.
I'm not very good with this.
What is probably the problem?
This is my index.php
require_once 'db.php';
$query = "SELECT * FROM quotes ORDER BY rand() LIMIT 1";
$result = mysqli_query($con, $query);
while($row = mysqli_fetch_array($result)) {
print(json_encode($row['quote']));
}
And this is my db.php
// Create connection
$con=mysqli_connect("host","user","pass","a6361246_phrases");
// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

Answer 1

You can use the first three lines in your db.php file like this...
<?php
$host = 'localhost'; $db = 'database-name'; $user = 'database-user'; $pw = 'database-password';
$conn = new PDO('mysql:host='.$host.';dbname='.$db.';charset=utf8', $user, $pw);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
?>
Don't forget to change database-name, database-user & database-password to your specific credentials.
Then using PDO get your phrase like this...
<?php
require_once 'db.php';
try {
$sql = "SELECT * FROM Quotes ORDER BY rand() LIMIT 1";
$query = $conn->prepare($sql);
$query->execute();
$row = $query->fetch(PDO::FETCH_ASSOC);
} catch (PDOException $e) {
die("Could not get the data: " . $e->getMessage());
}
?>