add_filter( 'posts_where' , 'posts_where_sqanda' );
function posts_where_sqanda( $where )
{
    global $wpdb;
    if( is_home() )
    {
        if( isset( $_GET[ 'noanswer' ] ) && !empty( $_GET[ 'noanswer' ] ) )
        {
            $comment_count = get_query_var( 'comment_count' );
            if( is_numeric($comment_count) )
             $where .= $wpdb->prepare( " AND {$wpdb->posts}.comment_count = %d ", $comment_count );
        }
    }
    //print $where;
    return $where;

}