It's pretty easy to query posts from one category but what if I need also one single post from another category?
$query = new WP_Query( 'cat=4' );
I'm looking for something like this:
$query = new WP_Query( array( 'cat' => 4, 'post__in' => array( 20 ) ) );
But the above code will not return anything because there are not posts with an ID of 20 in category 4. I'm wondering if anyone has any idea how this could be done.