Ajax in Wordpress

wp_plugin_ajax.php

<?php
/**
 * @package Quick Contact
 * @version 0.1
 */
/*
Plugin Name: Quick Contact
Plugin URI: http://techslides.com/
Description: Quick Contact WordPress Plugin to make an Ajax form submission, store it in the database, and show it in a Admin backend page.
Version: 0.1
Author URI: http://techslides.com/
*/

register_activation_hook(__FILE__,'qc_install');
register_deactivation_hook(__FILE__, 'qc_uninstall' );

global $jal_db_version;
$jal_db_version = "1.0";

function qc_install() {
  global $wpdb;
  global $jal_db_version;

  $table_name = $wpdb->prefix . "quickcontact";

  //http://codex.wordpress.org/Creating_Tables_with_Plugins
  $sql = "CREATE TABLE $table_name (
    id mediumint(9) NOT NULL AUTO_INCREMENT,
    time datetime DEFAULT '0000-00-00 00:00:00' NOT NULL,
    name VARCHAR(120) NOT NULL,
    email VARCHAR(120) DEFAULT '' NOT NULL,
    message text NOT NULL,
    UNIQUE KEY id (id)
  );";

  require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
  dbDelta($sql);

  add_option("jal_db_version", $jal_db_version);

}

function qc_uninstall() {
  global $wpdb;
  global $jal_db_version;

  $table_name = $wpdb->prefix . "quickcontact";

  $wpdb->query("DROP TABLE IF EXISTS $table_name");

  require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
  dbDelta($sql);
}

//http://codex.wordpress.org/Shortcode_API
function function_qc_form(){
  $html = '<div id="qc_form">
    <form id="ContactForm" action="" onsubmit="qc_process(this);return false;">
      <p>
        <label>Name</label>
        <input id="name" name="name" maxlength="120" type="text" autocomplete="off"/>
      </p>
      <p>
        <label>Email</label>
        <input id="email" name="email" maxlength="120" type="text" autocomplete="off"/>
      </p>
      <p>
        <label>Message</label>
        <textarea id="message" name="message" cols="6" rows="5" autocomplete="off"></textarea>
      </p>
      <p class="submit">
        <input id="send" type="submit" value="Submit"/>
      </p>
    </form>
  </div>
  <script>
    function qc_process(e){

      var data = {
          action: "my_qc_form",
          name: e["name"].value,
          email:e["email"].value,
          message:e["message"].value
      };

      jQuery.post("'.admin_url("admin-ajax.php").'", data, function(response) {
          jQuery("#qc_form").html(response);
      });

    }
  </script>
  ';
  return $html;
}
add_shortcode( 'qc_form', 'function_qc_form' );

//http://codex.wordpress.org/AJAX_in_Plugins
add_action('wp_ajax_nopriv_my_qc_form', 'my_qc_form_callback');
add_action('wp_ajax_my_qc_form','my_qc_form_callback');

function my_qc_form_callback() {
  global $wpdb; // this is how you get access to the database

   $table_name = $wpdb->prefix . "quickcontact";

  $name = $_POST['name'];
  $email = $_POST['email'];
  $message = $_POST['message'];


  $rows_affected = $wpdb->insert( $table_name, array( 
    'id' => null, 
    'time' => current_time('mysql'),
    'name' => $name,
    'email' => $email,
    'message' => $message
  ));


  if($rows_affected==1){
    echo "Your message was sent.";
  } else {
    echo "Error, try again later.";
  }

  die(); // this is required to return a proper result
}
?>