Php将空白数据插入表中

Question

My code inserts an empty record into the MySQL table "activate" instead of getting the data activate.html. It calls upon activate.php which I stripped down. I also should add that I am new to php, but am aware of injection attacks. I originally had some of the security issues addressed, but as I said, have stripped down the code to get to the root of the problem. Also, when I echo the form fields, they populate, just not into the MySql table. Any ideas why? Thank you in advance.

<?php
$host = "host"; // Host name
$username = "user"; // Mysql username
$password = "pass"; // Mysql password
$db_name = "db"; // Database name
$tbl_name = "activate"; // Table name

// Connect to server and select database.

mysql_connect("$host", "$username", "$password") or die("cannot connect");
mysql_select_db("$db_name") or die("cannot select DB");

// Get values from form

if (isset($_POST['submit'])) {
    $esn = mysql_real_escape_string($_POST['esn']);
    $esnverify = mysql_real_escape_string($_POST['esnverify']);
    $zip = mysql_real_escape_string($_POST['zip']);
    $comments = mysql_real_escape_string($_POST['comments']);
}

// Insert data into mysql

$sql = "INSERT INTO $tbl_name (esn, esnverify, zip, comments) VALUES ('$esn', '$esnverify', '$zip', '$comments')";
$result = mysql_query($sql);

// if successfully insert data into database, displays message "Successful".

if ($result) {
    echo "Successful";
    echo "<br />";
    echo $_POST['esn'];
    echo "<br />";
    echo $_POST['esnverify'];
    echo "<br />";
    echo $_POST['zip'];
    echo "<br />";
    echo $_POST['comments'];
    echo "<br />";
    echo "<a href='thankyou.html'>Back to main page</a>";
}
else {
    echo "ERROR";
}

?> 

    <?php

// close connection

mysql_close();
?>

Activate.html

<form method="post" action="activate.php">
<p><b>ESN:</b> <input type="text" id="esn" name="esn" maxlength="50"><br/>
<b>Confirm ESN:</b> <input type="text" name="esnverify" id="esnverify" maxlength="50"><br/>
<b>Zip:</b> <input type="text" name="zip" id="zip" maxlength="5"><br/>

<p>Your comments:<br />
<textarea name="comments" rows="10" cols="40" id="comments" maxlength="500"></textarea></p>

<p><input type="submit" value="Send it!"></p></form>

Answer 1

   <?php
$host = "host"; // Host name
$username = "user"; // Mysql username
$password = "pass"; // Mysql password
$db_name = "db"; // Database name
$tbl_name = "activate"; // Table name

// Connect to server and select database.

mysql_connect("$host", "$username", "$password") or die("cannot connect");
mysql_select_db("$db_name") or die("cannot select DB");

// Get values from form

if (isset($_POST['submit'])) {
    $esn = mysql_real_escape_string($_POST['esn']);
    $esnverify = mysql_real_escape_string($_POST['esnverify']);
    $zip = mysql_real_escape_string($_POST['zip']);
    $comments = mysql_real_escape_string($_POST['comments']);


// Insert data into mysql

$sql = "INSERT INTO $tbl_name (esn, esnverify, zip, comments) VALUES ('$esn', '$esnverify', '$zip', '$comments')";
$result = mysql_query($sql);

// if successfully insert data into database, displays message "Successful".

if ($result) {
    echo "Successful";
    echo "<br />";
    echo $_POST['esn'];
    echo "<br />";
    echo $_POST['esnverify'];
    echo "<br />";
    echo $_POST['zip'];
    echo "<br />";
    echo $_POST['comments'];
    echo "<br />";
    echo "<a href='thankyou.html'>Back to main page</a>";
}
else {
    echo "ERROR";
}

}

?> 

    <?php

// close connection

mysql_close();
?>

Also, change this in html code:

add name='submit' to input field/submit button.