PHP在DB中插入重复项

我正在尝试构建一个注册页面,当前代码正确运行,但我在数据库端获得了重复插入.我已经研究过并尝试了几种不同的解决方案,但还没有任何解决方案.我希望它很简单,我想念它.如何防止当前代码插入两次？

<?PHP
session_start();
$error=''; // Variable To Store Error Message
if (isset($_POST['register'])) {
//if (empty($_POST['email']) || empty($_POST['hash'])) {
//$error = "<br /> <p style='font-family:talo; color:red; margin-top:10px; font-size:16px;'>* Username or Password is invalid</p>";
//}
//else
//{
// Define all labels on the register form
$firstName=$_POST['firstName'];
$lastName=$_POST['lastName'];
$title=$_POST['title'];
$suffix=$_POST['suffixOne'];
$suffixTwo=$_POST['suffixTwo'];
$email=$_POST['email'];
$employer=$_POST['employer'];
$expertise=$_POST['expertise'];
$hash=$_POST['password'];
$confirmHash=$_POST['passwordConfirm'];
$primaryAddress=$_POST['primaryAddress'];
$secondaryAddress=$_POST['secondaryAddress'];
$city=$_POST['city'];
$state=$_POST['state'];
$zip=$_POST['zip'];
$country=$_POST['country'];
$primaryPhone=$_POST['primaryPhone'];
$secondaryPhone=$_POST['secondaryPhone'];

$connection = MysqLi_connect("localhost", "username", "password","DB");


$register = "INSERT INTO user (userID, firstName, lastName, title, suffix, suffixTwo, email, employer, expertise, primaryAddress, secondaryAddress, primaryPhone, secondaryPhone, city, postalCode, hash) 
VALUES (DEFAULT, '$firstName', '$lastName', '$title', '$suffix', '$suffixTwo', '$email', '$employer', '$expertise', '$primaryAddress', '$secondaryAddress', '$primaryPhone', '$secondaryPhone', '$city', '$zip', '$hash')";
if (MysqLi_query($connection, $register)) {
   header('Location: index.PHP');
}
MysqLi_close($connection);
}
?>

解决方法:

如果刷新页面,或者某人使用“后退”按钮再次点击该页面,则数据将重新发送到服务器,从而插入两次.您需要使用POST / REDIRECT / GET模式将用户重定向到另一个页面或同一页面以避免这种情况.发送303 HTTP响应将告诉浏览器在其历史记录中替换该页面,并避免重新发送发布的数据.

if (MysqLi_query($connection, $register)) {
    header('Location: index.PHP', true, 303);
    exit;
}