if (!($_GET['oblast-param'] && $_GET['work-param'] && $_GET['year-param'])) {
      $searchparam = array(
        'numberposts' => 12,
        'orderby'     => 'date',
        'order'       => 'DESC',
        'post_type'   => 'post',
       );
      } 

      if ($_GET['oblast-param'] && $_GET['work-param'] && $_GET['year-param']){
      $searchparam = array(
        'numberposts' => 12,
        'category__and' => array($_GET['oblast-param'], $_GET['work-param'], $_GET['year-param']),
        'orderby'     => 'date',
        'order'       => 'DESC',
        'post_type'   => 'post',
       );
      } 

$allposts = get_posts( $searchparam );
$posts = get_posts( $searchparam );

if (count($allposts)==0) {
        echo "Нічого не знайдено";
      } else {
      
      foreach( $posts as $post ){
        ?><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>" class="catalog-object-element">
          <?php the_post_thumbnail('thumbnail') ?>
          <span><?php the_title(); ?></span>
        </a><?php
      }