PHP 电子邮件订阅验证并检查现有

我正在用PHP创建一个电子邮件订阅表单，并想检查一个有效的地址以及电子邮件是否已经存在于我的数据库中。

代码正在连接到我的数据库并插入，但验证以及检查现有电子邮件不起作用。

无论我在表单中键入什么内容，即使我不键入任何内容，它也会将其插入我的数据库中。

这是我的所有代码：

<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
<fieldset>
<legend>Subscribe to Our Newsletter &nbsp;</legend>
<?php if ($feedback!='')
echo('<p>'.$feedback.'</p>'); ?>
<label>Name: <input name="name" type="text" value="<?php echo $name; ?>" /></label>
<label>Email: <input name="email" type="text" value="<?php echo $email; ?>" /></label> 
<label><input type="submit" value="Sign Up!" /></label>
</fieldset>
</form>
<?php

$feedback='';
if (!$email) {
$feedback .= '<strong>Please enter your email address</strong><br />';
}
if (!$name) {
$feedback .= '<strong>Please enter your name</strong><br />';
}

list($username, $mailDomain) = explode("@", $email);
if (!@checkdnsrr($mailDomain, "MX")) {

$feedback .= '<strong>Invalid email domain</strong><br />';
}

if(!preg_match("/^[_a-z0-9-]+('.[_a-z0-9-]+)*@[a-z0-9-]+('.[a-z0-9-]+)*('.[a-z]{2,3})$/", $email)) {

$feedback .= '<strong>Your email address doesn''t appear to be valid - please check and try again';
}

function cleaninput($value, $DB) {
    if (get_magic_quotes_gpc()) {
        $value = stripslashes( $value );
}
return mysql_real_escape_string( $value, $DB );
}

$name=$_POST['name'];
$email=$_POST['email'];
include_once "connect.php";

$sql = mysql_query("SELECT * FROM subscribers WHERE email='$email'");
$numRows = mysql_num_rows($sql);
    if ($numRows>0) {

$feedback = '<strong>That email address is already subscribed.</strong>';
}
$insertresult = mysql_query("INSERT INTO subscribers (name, email) VALUES('$name', '$email')") or die (mysql_error());

    if ($insertresult) {
        $completed = true;
    }

if($competed=false) {
?>
<form action="<?php echo $_SERVER['PHP_SELF']; ?> method="post">
        <fieldset>
    <legend>Subscribe to OUr Newsletter &nbsp;</legend>
<?php 
if ($feedback!='')
    echo('<p>'.$feedback.'</p>'); ?>
<label>Name: <input name="name" type="text" value="<?php echo $name; ?>" /></label>
<label>Email: <input name="email" type="text" value="<?php echo $email; ?>" /></label>
<label><input type="submit" value="Sign Up!" /></label>
        </fieldset>
</form>
<?php
}
else {

echo('Thanks - you have subscribed to our newsletter successfully. You can unsubscribe at any time by clicking the link at the bottom of each email we send.');
}

?>

此外，我的脚本中的最后一个回声总是在那里。它始终显示在我的表单下。不知道为什么会这样。也许我把它放在了代码中的错误位置。

else {

echo('Thanks - you have subscribed to our newsletter successfully. You can unsubscribe at any time by clicking the link at the bottom of each email we send.');
}

谢谢！