How to convert mysql data base table data in json using php

How to convert MySQL data base table into JSON data using PHP. Is there any way to do this?

Below is the php code I am using:

<?php 
$host = "emriphone.db.6420177.hostedresource.com"; 
$user = "emriphone"; 
$pass = "Light12-"; 
$database = "emriphone"; 

$linkID = mysql_connect($host, $user, $pass) or die("Could not connect to host."); 
mysql_select_db($database, $linkID) or die("Could not find database."); 

$sth = mysql_query("SELECT * FROM ProviderAppointmentListings");
$rows = array();
while($r = mysql_fetch_assoc($sth)) {
   $rows[] = $r;
}
print json_encode($rows);
?>