如果要使用COUNT(*)，则必须使用GROUP BY，但是您可以像这样使用mysql_num_rows()获取行数.>

You have to use GROUP BY if you want to use COUNT(*), but you can get the number of rows with mysql_num_rows() like this.

$result=mysql_query("SELECT * AS Result FROM users WHERE user_name='$user_name' AND pass='$password_hash' LIMIT 1") or die(mysql_error());
$num_rows = mysql_num_rows($result);