php - 无法识别的情况

Question

我有这个代码:

mysql_connect('localhost', 'user', 'pass');
            mysql_select_db('db');
    $$checkusername = mysql_query("SELECT `Username` FROM `users` WHERE `EmailAddress` = '".$email."'");
 if(mysql_num_rows($checkusername) == 1)
 {
    echo "<SCRIPT LANGUAGE='JavaScript'>
    window.alert('Sorry, that username is taken. Please go back and try again.')
    </SCRIPT>";
 }
 else
 {
echo 'Username Available';
}

实际上，用户名不可用，但仍然回显“用户名可用”。我也试过了，但还是一样:

mysql_query("SELECT * FROM `users` WHERE `EmailAddress` = '".$email."'");

我不知道我哪里错了。

Answer 1

去掉双美元符号:

   $$checkusername = mysql_query("SELECT `Username` FROM `users` WHERE `EmailAddress` = '".$email."'");

应该是

   $checkusername = mysql_query("SELECT `Username` FROM `users` WHERE `EmailAddress` = '".$email."'");