title: Query for find Posts don't have custom fields
body: <p>I write this Query to find posts that have custom field 'language' that value of it is 'English' OR Posts don't have custom field 'language' at all.</p>
  
  <pre><code>SELECT DISTINCT wp_posts.* FROM wp_posts, wp_postmeta 
  WHERE wp_posts.ID = wp_postmeta.post_id  
  AND (wp_postmeta.meta_key = 'language' AND wp_postmeta.meta_value like '%English%' OR NOT EXISTS (SELECT * FROM wp_posts, wp_postmeta Where wp_postmeta.meta_key = 'language' ))
  </code></pre>
  
  <p>But, it return only posts that have custom field 'language' and value of it is 'English'</p>
  
  <p>Please help me</p>