Resource for WHMCS MySQL database connection

There may be a time when you need to know the database resource variable for the default WHMCS MySQL connection. This variable is named $whmcsmysql, below is a quick example of how to use it.

global $whmcsmysql;
$query = sprintf("SELECT * FROM tblclients WHERE id = %d", $_REQUEST['id']);
$result = mysql_query($query, $whmcsmysql);
if($result === false) die('Query Failed: ' . mysql_error());
$client = mysql_fetch_assoc($result);
if(!is_array($client)) die("No client found with id " . $_REQUEST['id']);