Conditional Meta Data or Custom Fields

This can be done using filters on the query. Here is an article with some sample code that might help:
https://wordpress.mcdspot.com/2013/01/25/sort-on-presence-of-custom-field-field-value-then-date/

Wow, this is way above my head. Let me try to make it simpler,

How can I query for all posts in a post type where a field is not null? I’m using this at the moement:

<?php
	$args = array(
		'posts_per_page' => -1,
		'order' => 'ASC',
		'orderby' => 'title',
		'post_type' => 'store'
		);
		query_posts($args); if (have_posts()) : ?>
	<?php while (have_posts()) : the_post(); ?>
		 <p class="directory">
		  <a href="<?php echo get_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></p>
   <?php endwhile; ?>
  <?php else : ?>
		<h3 class="post-title">No Stores Found</h3>
		<p>We're sorry, but there are no stores currently available for display. Please return soon.</p>
		<p>
		  <a href="<?php echo get_option('home'); ?>">Return to the homepage</a></p>
<?php endif; wp_reset_query(); ?>

I think if I can see how to return posts where the field is null (and when it is not null as well), I should be fine.

Thanks

OK, I’ll try to make it simpler. Just change this:

<?php
	$args = array(
		'posts_per_page' => -1,
		'order' => 'ASC',
		'orderby' => 'title',
		'post_type' => 'store'
		);

to this:

<?php
   // Sort posts in order on presence of a custom field,
   // value of custom field, then date
   $meta_key = 'auteur';  // The meta_key

   // NOTE: The functions and add_filter() calls should really go in functions.php,
   //       but they will work here and are included here for convenience.
   function mam_posts_fields ($fields) {
       global $mam_global_fields;
       // Make sure there is a leading comma
       if ($mam_global_fields) $fields .= (preg_match('/^(\s+)?,/',$mam_global_fields)) ? $mam_global_fields : ", $mam_global_fields";
       return $fields;
    }
    function mam_posts_join ($join) {
       global $mam_global_join;
       if ($mam_global_join) $join .= " $mam_global_join";
       return $join;
    }
    function mam_posts_where ($where) {
       global $mam_global_where;
       if ($mam_global_where) $where .= " $mam_global_where";
       return $where;
    }
    function mam_posts_orderby ($orderby) {
       global $mam_global_orderby;
       if ($mam_global_orderby) $orderby = $mam_global_orderby;
       return $orderby;
    }
    add_filter('posts_fields','mam_posts_fields');
    add_filter('posts_join','mam_posts_join');
    add_filter('posts_where','mam_posts_where');
    add_filter('posts_orderby','mam_posts_orderby');

    global $wpdb,$wp_query;
    $mam_global_fields = ', IF(ISNULL(pm.meta_id),9,1) as sort_key, pm.meta_value';
    $mam_global_join = " LEFT JOIN $wpdb->postmeta pm ON ($wpdb->posts.ID = pm.post_id AND pm.meta_key = '$meta_key')";
    $mam_global_orderby = "sort_key, pm.meta_value, $wpdb->posts.post_date DESC";

$args = array(
   'posts_per_page' => -1,
   'post_type' => 'store'
);

And put in your own key for $meta_key.

I really need to get better with PHP. Thanks for all your help so far. I tried the code above, modified the meta_key value, but the results weren’t sorted.

I was able to get it to work through a bit of a hack though, here’s how it looks, and here’s what I did:

<?php
	$args = array(
		'posts_per_page' => -1,
		'order' => 'ASC',
		'orderby' => 'title',
		'post_type' => 'store'
		);
		query_posts($args); if (have_posts()) : ?>
	<?php while (have_posts()) : the_post(); ?>
    <?php $value = get_post_meta($post->ID, 'store_meta_phone', true); ?>
		 <?php if($value != '') : ?>
         <p class="directory premium">
		  <a href="<?php echo get_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></p>
         <?php endif; ?>
   <?php endwhile; ?>
<?php endif; wp_reset_query(); ?>

<?php
	$args2 = array(
		'posts_per_page' => -1,
		'order' => 'ASC',
		'orderby' => 'title',
		'post_type' => 'store'
		);
		query_posts($args2); if (have_posts()) : ?>
	<?php while (have_posts()) : the_post(); ?>
    <?php $value2 = get_post_meta($post->ID, 'store_meta_phone', true); ?>
    	<?php if(empty($value2)) : ?>
		 <p class="directory">
		  <a href="<?php echo get_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></p>
          <?php endif; ?>
   <?php endwhile; ?>
  <?php else : ?>
		<h3 class="post-title">No Stores Found</h3>
		<p>We're sorry, but there are no stores currently available for display. Please return soon.</p>
		<p>
		  <a href="<?php echo get_option('home'); ?>">Return to the homepage</a>
		</p>
		<p>&nbsp;</p>
		<p>&nbsp;</p>
		<p>&nbsp;</p>
<?php endif; wp_reset_query(); ?>

Basically I’m displaying some stores as preferred if there is a phone number stored, and the rest after if no phone number is present by running two queries. Is this a bad practice?