我將如何停止多個電子郵件或用戶名？

Question

我在登記表，以防止對多個用戶名下面的代碼創建：

connect_db(); 
    $check = mysql_query("SELECT username FROM school_users WHERE username = '$username'") or die(mysql_error()); 
    $check2 = mysql_num_rows($check); 

if ($check2 != 0) { 
    respond("error", "Sorry, the username ".$_POST['username']." is already in use. Please choose a different username.");} 

不過，我也想檢查郵件，在同一個語句：

connect_db(); 
     $check = mysql_query("SELECT username, email FROM school_users WHERE username = '$username' or email = '$email'") or die(mysql_error()); 
     $check2 = mysql_num_rows($check); 

    if ($check2 != 0) { 
if (???username???){ 
     respond("error", "Sorry, the username ".$_POST['username']." is already in use. Please choose a different username.");}} 
else if (???email???) { 
    respond("error", "Sorry, the username ".$_POST['username']." is already in use. Please choose a different username.");}} 

Answer 1

你可以嘗試做：

connect_db(); 
$check = mysql_query("SELECT 'User' validation 
         FROM school_users 
         WHERE username = '$username' 
         UNION ALL 
         SELECT 'Email' 
         FROM school_users 
         WHERE email = '$email'") or die(mysql_error()); 
$row = mysql_fetch_assoc($check); 

if($row) 
{ 
    if ($row["validation"] == 'User') { 
      respond("error", "Sorry, the username ".$_POST['username']." is already in use. Please choose a different username.");}} 
    else if ($row["validation"] == 'Email') { 
     respond("error", "Sorry, the email ".$_POST['email']." is already in use. Please choose a different email.");}} 
} 

或者您也可以單獨做到這一點...

//Validate UserName 
connect_db(); 
$check = mysql_query("SELECT username FROM school_users WHERE username = '$username'") or die(mysql_error()); 
$check2 = mysql_num_rows($check); 

if ($check2 != 0) { 
    respond("error", "Sorry, the username ".$_POST['username']." is already in use. Please choose a different username.");} 

//Validate Email 
connect_db(); 
$checkEmail = mysql_query("SELECT email FROM school_users WHERE email = '$email'") or die(mysql_error()); 
$checkEmail2 = mysql_num_rows($check); 

if ($checkEmail2 != 0) { 
    respond("error", "Sorry, the email ".$_POST['email']." is already in use. Please choose a different email.");} 

此外，您的代碼容易受到SQL注入攻擊，並且您正在使用不推薦使用的MySQL php函數。如果你想使你的代碼更好的那麼脆弱，一起來看看下面的鏈接：

Why shouldn't I use mysql_* functions in PHP?

What could i use instead of mysql_ functions?

Prepated Statements

Prepared Statements with MySQLi

Answer 2

你也可以做到這一點在一個聲明中：

SELECT username 
FROM school_users 
WHERE username = '$username' or email = '$email' 

如果你這樣做，你需要改變消息給用戶。 。 。 「您的用戶名或電子郵件（或兩者）已被使用」。

要在一個聲明自定義消息，你可以使用聚合：

select (case when max(username = '$username') = 1 and max(email = '$email' = 1 
      then 'both' 
      when max(username = '$username') = 1 
      then 'username' 
      when max(email = $email) = 1 
      then 'email' 
     end) as WherePresent 
from school_users 
WHERE username = '$username' or email = '$email' 

這將返回0行，如果一切正常。否則，它會返回一行，其中包含「both」，「username」，「email」之一，表明哪一個是重複的。

Answer 3

最初的代碼並不像您想象的那麼遠。

$check = mysql_query("SELECT username, email FROM school_users WHERE username = '$username' or email = '$email' LIMIT 1") or die(mysql_error()); //Limit one reduces the time mysql searches the db since it stops on the first occurence 
     $check2 = mysql_fetch_assoc($check); //we do not only want to know the count of matching rows, but the values return in email and username field 

//trimming makes sure we do not have any spaces at the beginning or end 
//strtolower makes sure we set UserName == usERnaME == username etc.pp. 
if (strtolower(trim($row['username'])) == strtolower(trim($_POST['username']))){ // check the result 
     respond("error", "Sorry, the username ".$_POST['username']." is already in use. Please choose a different username.");} 
} 
else if (strtolower(trim($row['email'])) == strtolower(trim($_POST['email']))) { // and again for email adress 
    respond("error", "Sorry, the email ".$_POST['email']." is already in use. Please choose a different email.");} 
}