functions.php

<?php
add_action("wp_enqueue_scripts", "my_enqueue", 11);
function my_enqueue() {
	wp_deregister_script('jquery');
	wp_register_script('jquery', "http" . ($_SERVER['SERVER_PORT'] == 443 ? "s" : "") . "://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js", false, null);
	wp_enqueue_script('jquery');
	wp_enqueue_script( 'function', get_stylesheet_directory_uri().'/js/gallery_script.js', 'jquery', true);
}

// add actions to respond to get_gallery_data
add_action("wp_ajax_nopriv_get_gallery_data", "get_gallery_data");
add_action("wp_ajax_get_gallery_data", "get_gallery_data");

// define the get_gallery_data function that retrieves records from the database
function get_gallery_data() {

    if ( !wp_verify_nonce( $_REQUEST['nonce'], "my_gallery_nonce")) {
        exit("No naughty business please");
    }

    // build your SQL up using the request parameters, for example, $_REQUEST["occasion_id"]
    $query = "SELECT id, occasion, size FROM cakes WHERE occasion = " . $_REQUEST["occasion_id"];

    // issue the query
    global $wpdb;
    $query_result = $wpdb->get_results($query, OBJECT);
    $result['type'] = "success";
    $result['data'] = $query_result;

    // encode result as JSON and return it
    $result = json_encode($result);
    echo $result;

    die();
}
?>