Meta Query within a Meta Query?

Question

I'm trying to query 'live' posts for 'venue' field existing (venue field is ID's of venue pages). Query those venue IDs/posts for which ones have a field 'country' that's value (ID) matches a specific country value.

$shows = get_posts(array(
    'post_type' => 'live',
    'meta_query' => array(
        array(
            'meta_key' => 'venue',
                'meta_query' => array(
                    array(
                        'meta_key' => 'country',
                        'value' => 'country_1',
                    )
                )
            )
    )

));

Answer 1

WP_Query isn't designed to make such query-in-query logic. It should have one single post_type, one single meta_query.

That's why you need to use 2 queries instead.

$live_posts = new WP_Query( array (
     'post_type'=> 'live'
     'posts_per_page'        => -1,
         'meta_key'=>'venue_key_name',
         'meta_value'=>'venue_key_value',
     'fields' => 'ids'
 ));

$venue_posts=get_posts(array(
    'post_type'=>'venue',
    'meta_key'=>'country_meta_name',
    'meta_value'=> $live_posts->posts,
    'meta_compare'=>'IN'
));

In the given code you need to change meta key and values of course.

Update:

If your input parameter is array of venue IDs and your output is supposed to be country posts of those venues, then you can use these queries below:

global $wpdb;

$countries=$wpdb->get_col("SELECT meta_value FROM $wpdb->postmeta 
WHERE meta_key='country' AND post_id IN (".implode(",",$array_of_venue_page_ids).")");

if(empty($countries))$countries=[0];

$live_posts = new WP_Query( array (
     'post_type'=> 'live'
     'post__in' => $countries,
 ));