functions.php

<?php
function justin_search_join( $join ) {
        global $wpdb;
        if( is_search() && !is_admin()) {
                $join .= "LEFT JOIN $wpdb->postmeta AS m ON ($wpdb->posts.ID = m.post_id) ";
        }
        return $join;
}
// uncomment this to add this functionality
//add_filter('posts_join', 'justin_search_join' );
function justin_search_groupby( $groupby ) {
        global $wpdb;
        if( is_search() && !is_admin()) {
                $groupby = "$wpdb->posts.ID";
        }
        return $groupby;
}
// uncomment this to add this functionality
//add_filter('posts_groupby', 'justin_search_groupby' );
function justin_search_where( $where ) {
        global $wpdb, $wp_query;
        if( is_search() && !is_admin()) {
                $where = "";
                $search_terms = se_get_search_terms();
                $n = !empty($wp_query->query_vars['exact']) ? '' : '%';
                $searchand = '';
                if (count($search_terms) < 1) {
                        // no search term provided: so return no results
                        $search = "1=0";
                } else {
                        foreach( $search_terms as $term ) {
                                $term = esc_sql( like_escape( $term ) );
                                $search .= "{$searchand}(($wpdb->posts.post_title LIKE '{$n}{$term}{$n}') OR ($wpdb->posts.post_content LIKE '{$n}{$term}{$n}') OR (m.meta_value LIKE '{$n}{$term}{$n}'))";
                                $searchand = ' AND ';
                        }
                }
                $where .= " AND ${search} ";
                $where .= " AND (m.meta_key IN ('_ENTER_KEY_HERE')) ";
                $where .= " AND ($wpdb->posts.post_password = '') ";
                $where .= " AND ($wpdb->posts.post_type IN ('post', 'page', '__ENTER_CUSTOM_POST_TYPE_HERE')) ";
                $where .= " AND ($wpdb->posts.post_status = 'publish') ";
        }
        return $where;
}
// uncomment this to add this functionality
//add_filter('posts_where', 'justin_search_where' );
// Code from Search Everywhere plugin
function se_get_search_terms()
{
        global $wpdb, $wp_query;
        $s = isset($wp_query->query_vars['s']) ? $wp_query->query_vars['s'] : '';
        $sentence = isset($wp_query->query_vars['sentence']) ? $wp_query->query_vars['sentence'] : false;
        $search_terms = array();

        if ( !empty($s) )
        {
                // added slashes screw with quote grouping when done early, so done later
                $s = stripslashes($s);
                if ($sentence)
                {
                        $search_terms = array($s);
                } else {
                        preg_match_all('/".*?("|$)|((?<=[\\s",+])|^)[^\\s",+]+/', $s, $matches);
                        $search_terms = array_map(create_function('$a', 'return trim($a, "\\"\'\\n\\r ");'), $matches[0]);
                }
        }
		
        return $search_terms;
}