我应该如何在PHP中的类中调用mysql数据库函数？

Question

This is something I've struggled with for some time now, and I know I'm not alone. I'm looking for a "best practice" way to be able to use a database connection in my PHP classes. I've just started to read about static functions and singletons. I currently think this is the way to go, but I want to avoid seeing every problem as a nail just after buying a new hammer, if you know what I mean. I know I'm not the only person to query this, but I can't find a good resource that explains how it should be done.

What I think I'm looking for is a re-useable class that removes, or minimises, any global calls. I know that I don't want to make multiple copies of a class or create multiple database instances for performance reasons.

What I think I've made (and I'm a little fuzzy on the definitions of some of the words) is a database singleton.

What I'm looking for is some advice. Is this how I "should" be using a database class? If so, have I written it in the best way?

Here's the PHP:

<?php
# set all errors and notices on.
error_reporting(E_ALL);
ini_set('display_errors', '1');


# database static class.
class database {

    private static $connection;
    private static $instance;

    private function __construct(){
        # run the connection here
        self::$connection='*dbcon*';
        echo 'connecting...<br />';
    }

    public static function getInstance(){
        # this only runs once, calling the construct once.
        if(!self::$instance){
            self::$instance = new database();
        }
        return self::$instance;     
    }

    private static function sanitise($data){
        # sanitise data before it's sent to the database
        return '~'.$data.'~';
        # sanitisation is flagged by adding tildas to a string.
    }

    public function runquery($query){
        echo 'running query...<br />';
        return self::$connection.' - '.self::sanitise($query);
    }
}

# user class
class myuser {

    function getuser($username){
        # this uses the database class, but shouldn't call a second copy of it.
        # I should be able to re-use the connection string created outside this class.
        # Doing so sould not trigger a reconnection (flagged by echoing 'connecting...')
        echo database::runquery('SELECT * FROM user_tbl WHERE username='.$username);
        # The above line will call everything I need to return a result including sanitisation.
    }
}

# this line would be needed to substantiate an instance of the database.
database::getInstance();
# run two queries on the database to see if they both run from the same connection
echo database::runquery('test query');
echo '<br />';
echo database::runquery('second test query');
echo '<br />';

# substantiate a new user class
$user = new myuser();
# load in the current user.
$user->getuser('mark');
?>

And here's the results:

connecting...
running query...
*dbcon* - ~test query~
running query...
*dbcon* - ~second test query~
running query...
*dbcon* - ~SELECT * FROM user_tbl WHERE username=mark~

I only have one "connecting..." string in my output, and I can call a database query from anywhere without calling something like $this->database = new database(); in the constructor of each and every class I make.