connection mySQL

I have following code to connect MySQL server. I got Connected to database message, but I got Could not run query : No database selected error message when run mysql_query. I check that the database name is correct, I use root account which should have the rights to do select. I can access my db using phpMyAdmin, so my PHP and MySQL server both running. It seems that it connected to MySQL, but for some reason it does not connect to the database. Are there any configuration need to check for the connection? Your help and information is great appreciated, $hostname = "localhost"; $username = "MyUser"; $password = "mypassword"; try { $dbh = new PDO("mysql:host=localhost;dbname=mydb;charset=utf8", $username, $password);

      echo "Connected to database";
    }

catch(PDOException $e) { echo $e->getMessage();

    }

$result = mysql_query("SELECT invid, invdate, note, amount FROM invheader"); if (!$result) { echo 'Could not run query: ' . mysql_error(); exit; }