检查MySQL结果是否以PHP返回的最佳方法?

我正在寻找检查并查看查询是否返回任何结果的最佳方法.我觉得我经常写这部分代码，有时会出错，有时却没有.

I'm looking for the best way to check and see if any results were returned in a query. I feel like I write this part of code a lot and sometimes I get errors, and sometimes I don't.

例如，我运行此查询以检查是否存在用户名，然后再将新用户名插入数据库.

For example, I run this query to check if a username exists before inserting a new one into the database.

$result = mysql_query("SELECT * FROM ...");

然后，我要检查是否返回了任何结果.这是我这样做的一种方式:

Then I want to check and see if any results were returned. Here is one way I do it:

if (!$result) { PERFORM ACTION }

如果第一种方法不起作用，那么有时会:

If the first way doesn't work, then sometimes this will:

if (mysql_num_rows($result)==0) { PERFORM ACTION }

然后我什至看到有一天我可以这样做:

Then I even saw that I could do it this way the other day:

list($total) = mysql_fetch_row($result);
if ($total==0) { PERFORM ACTION }

做到这一点的最佳方法是什么?

What is the best way to do this?