title: Display results of one meta key and order by a different meta key
body: <p>On a used car dealership website, I have a PHP Query that displays all results for the relevant vehicle model. So if you visit the "Honda Civic" page it will display all the vehicles listed as a Civic.</p>
  
  <p>Currently, I'm using the following query:</p>
  
  <pre><code>$paged = (get_query_var('paged')) ? get_query_var('paged') : 1; 
  $args = array(
    'post_type' =&gt; array('vehicle'), 
    'post_status' =&gt; 'publish', 
    'orderby' =&gt; 'date',
    'order' =&gt; 'ASC',  
    'posts_per_page' =&gt; 10, 
    'paged' =&gt; $paged,
    'meta_key' =&gt; 'model',
    'meta_value' =&gt; $model,
  );
  </code></pre>
  
  <p>This works as expected, however I would like to sort the result so that it displays used vehicles first and demo vehicles second. So I need to order the results by the "Demo" meta key, while still displaying only the relevant models.</p>
  
  <p>I've tired the query below based on another StackOverflow question's answer, but it returns no results:</p>
  
  <pre><code>$paged = (get_query_var('paged')) ? get_query_var('paged') : 1; 
  $args = array(
    'post_type' =&gt; array('vehicle'),
    'post_status' =&gt; 'publish',   
    'meta_key' =&gt; 'Demo', 
    'orderby' =&gt; 'meta_value',
    'order' =&gt; 'ASC',
    'posts_per_page' =&gt; 10,
    'paged' =&gt; $paged,
    'meta_query' =&gt; array(
    array('key' =&gt; 'model', 'value' =&gt; '$model')
    )
  );
  </code></pre>
  
  <p>Any help would be appreciated.</p>
  
  <p>Thanks in advance<br>
  Willem</p>