custom search

if( !is_admin() ):
    add_filter('pre_get_posts','my_filter_the_search',10,1);
endif;

function my_filter_the_search($query){

    $general_site_search = filter_input(INPUT_GET, 's', FILTER_SANITIZE_STRING);

    if(!empty($general_site_search)):
        add_filter( 'posts_search', '__search_by_title_only', 500, 2 );
    endif;
}

function __adapted_search_function($search, $query) {
  if(is_admin() || !$query->is_main_query() || !$query->is_search)
    return; //determine if we are modifying the right query

  global $wpdb;
  $search_term = $query->get('s');
  $search = ' AND (';

  //point 1
  $search .= "($wpdb->posts.post_title LIKE '%$search_term%')";

  //need to add an OR between search conditions
  $search .= " OR ";

  //point 2
  $search .= "($wpdb->posts.post_excerpt LIKE '%$search_term%')";

  //need to add an OR between search conditions
  $search .= " OR ";

  //point 3
  $search .= "($wpdb->postmeta.meta_key = 'mcb-product' AND $wpdb->postmeta.meta_value LIKE '%$search_term%')";

  //add the filter to join, sql will error out without joining the tables to the query
  add_filter('posts_join', '__custom_join_tables');

  return $search . ') ';
}

function __custom_join_tables($joins) {
  global $wpdb;
  $joins = "JOIN $wpdb->postmeta ON ($wpdb->postmeta.post_ID = $wpdb->posts.ID)";
  return $joins;
}