MySQL to MySQLi migration: easy backward compatibility

// MySQLi connection
$mysqli_link = mysqli_connect('HOST','USER','PASSWORD','DATABASE');
$mysqli_link->set_charset('utf8'); // if needed, depending on your configuration

// backward compatibility of old MySQL functions by rAthus
function mysql_connect() {
    return true;
}
function mysql_select_db() {
    return true;
}
function mysql_query($q) {
    global $mysqli_link;
    return mysqli_query($mysqli_link,$q);
}
function mysql_fetch_array($r) {
    return mysqli_fetch_array($r,MYSQLI_ASSOC);
}
function mysql_num_rows($r) {
    return mysqli_num_rows($r);
}
function mysql_error() {
    global $mysqli_link;
    return mysqli_error($mysqli_link);
}
function mysql_insert_id() {
    global $mysqli_link;
    return mysqli_insert_id($mysqli_link);
}
function mysql_close($mysqli_link) {
    global $mysqli_link;
    return mysqli_close($mysqli_link);
}

// if you have errors like "this is incompatible with sql_mode=only_full_group_by", try enabling this:
//mysqli_query($mysqli_link,'SET sql_mode=""');