<?php

function custom_posts_clauses($clauses) {
    global $wpdb;
    // Add a LEFT JOIN clause to include the _thumbnail_id for all posts
    $clauses['join'] .= " LEFT JOIN $wpdb->postmeta ON ($wpdb->posts.ID = $wpdb->postmeta.post_id AND $wpdb->postmeta.meta_key = 'recipe_gallery')";
    // Modify the ORDER BY clause to prioritize posts with featured images
    $clauses['orderby'] = "($wpdb->postmeta.meta_key IS NULL) ASC, " . $clauses['orderby'];
    return $clauses;
}

// Add the custom_posts_clauses function as a filter
add_filter('posts_clauses', 'custom_posts_clauses');
?>

<?php

remove_filter('posts_clauses', 'custom_posts_clauses');

?>