乍一看..您应该在执行查询之前选择 db .. 所以替换

 $sql = "SELECT * FROM   usergroups";
 mysql_select_db('dopetunez');

和

  mysql_select_db('dopetunez');
  $sql = "SELECT * FROM   usergroups";

建议请使用mysqli_和PDO 。mysql_不再维护

您应该首先选择数据库。然后只有您可以访问查询。请改成这样，

$conn = mysql_connect($dbhost, $dbuser, $dbpass);
mysql_select_db('dopetunez');

$sql = "SELECT * FROM   usergroups";