php - 防止重复数据进入mysql数据库

Question

我试图让我的电子邮件订阅服务拒绝我的数据库中已经存在的电子邮件，这样用户就不会订阅同一封电子邮件两次。这就是我所拥有的，但它不起作用，有什么想法吗？

<?php 
    if(!isset($_POST['submit'])) 
        exit();

    $vars = array('email');
    $verified = TRUE;
    foreach($vars as $v) {
        if(!isset($_POST[$v]) || empty($_POST[$v])) {
            $verified = FALSE;
        }
    }   
    if(!$verified) {
        echo "<p style='color:white; margin-top:25px;'>*Email required*</p>";
        exit();
    }
    $email = $_POST['email'];
    if($_POST['submit']) echo "<p style='color:white; margin-top:25px;'>*Check your inbox*        </p>";

    // Create connection
    $con=mysqli_connect("mysql.host","user","password","dbname");

    // Check connection
    if (mysqli_connect_errno($con))
    {
        echo "Failed to connect to MySQL: " . mysqli_connect_error();
    }

    $sql="INSERT INTO emails (email)    VALUES  ('$_POST[email]')";
    if (!mysqli_query($con,$sql))
    {
        die('Error: ' . mysqli_error($con));
    }

    $query = mysql_query("SELECT * FROM emails WHERE email='$email'",($con));
    if(mysql_num_rows($query) != 1)
    {
        echo "email already exists";
        // redirect back to form and populate with 
        // data that has already been entered by the user
    }


    mysqli_close($con);
?>

Answer 1

让 MySQL 拒绝重复电子邮件地址的最简单方法是使字段唯一 (http://www.w3schools.com/sql/sql_unique.asp)

ALTER TABLE emails ADD UNIQUE (email)

但是，MySQL 不会返回警告