检查这是否重复

检查这是否重复

问题描述：

我想检查username是否已经存在，如果存在则抛出错误消息，我该怎么做? 我已经尝试搜索，但是只找到mysql_errno，但对我不起作用.

I want to check if the username already exists and throw an error message if exist, any tips how can I do it? I've already tried to search but only found mysql_errno but it won't work for me.

  if ($valid) {
        $pdo = Database::connect();
        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        //$password = md5($password);
        $sql = "INSERT INTO users (username,password,role) values(?, ?, ?)";
        $q = $pdo->prepare($sql);
        $q->execute(array($username,$password,$role));
        Database::disconnect();
        header("Location: index.php");
    }

答

如果要检查username是否已使用:

If you want to check if the username is already used :

SELECT * FROM users WHERE username = :username

如果返回一行:抛出错误，否则执行INSERT

If you return one row : you throw your error, else you do your INSERT

因此您的代码应如下所示:

So your code should look like this :

if ($valid) {
    $pdo = Database::connect();
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $sql_check = "SELECT * FROM users WHERE username = :username";
    $test = $pdo->prepare($sql_check);
    $test->bindParam(':username', $username); 
    $test->execute;

现在这是两种解决方案，以检查是否有一行:

Now here is two solution to check if you have one row :

    if($test->rowCount() > 0) {
        // error
    }

或

    $user = $test->fetch();

    if (!empty($user)) {
        // error
    }

现在，如果您没有错误，请插入:

And now if you don't have error, do you insert :

    else {
        //$password = md5($password);
        $sql = "INSERT INTO users (username,password,role) values(?, ?, ?)";
        $q = $pdo->prepare($sql);
        $q->execute(array($username,$password,$role));
        Database::disconnect();
        header("Location: index.php");
    }
}

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