Returning a list of custom post types excluding those without a specific meta_value

Question

UPDATE: I think I'm on the right path with some of the help from the meta query options, but I might've gone overboard as it's extremely inefficient. You can see the updated code in the bottom of this post.

I technically have three questions for this, but they're related and require the first to be answered, so I hope it's okay to post all here.

To put this in a little context, I'm working on a directory of sorts where I can add to 3 URLs in 3 meta fields for each post. I want to display a list of only posts that have 1-3 of said URLs added. To make this extra interesting, I also have 3 corresponding checkboxes to each meta field that I can select in case an item is sold out. I would like to exclude sold out items from this list as well.

Question 1 - How do I display a list of custom post type posts that all have the same meta_value and key (excluding those that have the same value)

I've managed to make a list that returns all myPostType posts where 'meta_value' => false in myMetaKey. See code below:

<?php 
    $args = array(
        'post_type' => 'myPostType', 
        'meta_key' => 'myMetaKey', 
        'meta_value' => false, 
        'orderby' => '_custom', 
        'order' => 'ASC', 
        'posts_per_page' => -1, );
    $loop = new WP_Query($args);
    while ($loop->have_posts() ) : $loop->the_post();
?>

I am interested in having a list that returns posts that does have a meta_value in myMetaKey. I thought it would be as simple as to change false to true in meta_value, but that returns an empty list instead.

SOLVED: Question 2 - How do I return a list that includes posts with different meta_key's?

I'm interested in also having the list display posts from myPostType that have both myMetaKeyA, myMetaKeyB and myMetaKeyC - but only if meta_value is true (or the equivalent as asked above in questions 1).

Thanks to Niels who directed me to the meta_query class. Adding multiple arrays to meta_query did the trick.

Question 3 - How do I exclude posts that have a meta_key with a corresponding checkbox selected

As mentioned in the beginning I'm also interested in excluding posts via a selected checkbox.

---

I think I fixed a lot of my issues, but my code is so inefficient that it's practically useess.

As it is below it takes more than 30 mins. to load (as in I closed the tab after 30 mins.). Does anyone have any pointers as to how to rewrite this more efficiently?

<?php 
  $args = array(
    'post_type' => array('myPostType1', 'myPostType2'), 
    'orderby' => '_custom', 
    'order' => 'ASC', 
    'posts_per_page' => -1,
    'meta_query' => array( 'relation' => 'OR',
      array('relation' => 'AND',
          array(
            'key' => 'product1',
            'value' => false,
            'compare' => '!=',
            ),
          array(
            'key' => 'stock1',
            'value' => '"soldOut1"',
            'compare' => 'NOT LIKE',
            )
          ),
      array('relation' => 'AND',
          array(
            'key' => 'product2',
            'value' => false,
            'compare' => '!=',
            ),
          array(
            'key' => 'stock2',
            'value' => '"soldOut2"',
            'compare' => 'NOT LIKE',
            )
          ),
      array('relation' => 'AND',
          array(
            'key' => 'product3',
            'value' => false,
            'compare' => '!=',
            ),
          array(
            'key' => 'stock3',
            'value' => '"soldOut3"',
            'compare' => 'NOT LIKE',
            )
          )
        )
  );
  $loop = new WP_Query($args);
  while ($loop->have_posts() ) : $loop->the_post();
?>

Answer 1

Considering your current code I think you missed the WP Meta Query class which can do what you want;

https://codex.wordpress.org/Class_Reference/WP_Meta_Query