PHP5如何连接不上MySQL数据库

PHP5怎么连接不上MySQL数据库？
代码
$db_host='localhost';
$db_database='120422db_1';
$db_username='root';
$db_password='1234';

?>



include('120422php_1.php');

$connection = mysql_connect($db_host, $db_username, $db_password);
if(!$db_connection){
die ("Could not connect to the database:
". mysql_error());
}
?>


结果：Could not connect to the database:

------解决方案--------------------
if(!$db_connection){
用错了变量！
应该是 $connection