title: Simple WP Query upcoming events with start OR end date
body: <p>I'm working with an upcoming events list. I create a custom post type, with a custom field: event_start_date. I also have some multiday extension events, defined by an additional custom field: event_end_date .</p>
  
  <p>I have a code that work fine for events with a start_date later than today. But I fail incorporating the end_date condition. I try with a meta_query, with OR relation, that currently don't work:</p>
  
  <pre><code>$args = array(
      'post_type' =&gt; 'events',
      'posts_per_page' =&gt; 4,
      'orderby' =&gt; 'event_start_date',
      'order' =&gt; 'ASC',
      'meta_query' =&gt; array(
           'relation' =&gt; 'OR',
            array('key'  =&gt; 'event_start_date',
                'value' =&gt; date('m/d/Y', strtotime('-1 day')),
                'compare' =&gt; '&gt;='),
  
                array('key'  =&gt; 'event_end_date',
                    'value' =&gt; date('m/d/Y', strtotime('-1 day')),
                    'compare' =&gt; '&gt;=')
      )
  );
  $loop = new WP_Query( $args ); 
  while ( $loop-&gt;have_posts() ) : $loop-&gt;the_post();
  // Rest of the loop
  </code></pre>
  
  <p>Thanks in advance.</p>
  
  <p><strong>Note</strong>: I have this other query, that works perfect selecting events with only a start date > than current date.</p>
  
  <pre><code>                    $args = array(
                      'post_type' =&gt; 'events',
                      'posts_per_page' =&gt; 4,
                      'meta_key'  =&gt; 'event_start_date',
                      'meta_value' =&gt; date('m/d/Y', strtotime('-1 day')),
                      'meta_compare' =&gt; '&gt;=', 
                      'orderby' =&gt; 'event_start_date',
                      'order' =&gt; 'ASC',           
                      ); // The same loop and query
  </code></pre>