title: SQL show result if meta_key not exists or not is 1
body: <p>with the following SQL query I check whether a meta value of a (Wordress) post is not equal to 1. But I also want to check if the meta_key 'gtp_conversion_uploaded' exists. And if it not exists I still want to select the <code>ID</code>.</p>
  
  <pre><code>SELECT DISTINCT p.ID
  FROM wp_posts p
  LEFT JOIN wp_postmeta m2 ON m2.post_id = p.ID
  AND m2.meta_key = 'gtp_conversion_uploaded'
  AND m2.meta_value != 1
  </code></pre>
  
  <p>So my query needs to do the following checks:</p>
  
  <ul>
  <li>Select the results where meta_key 'gtp_conversion_uploaded' is not
  equal to 1.</li>
  <li>And also if the meta_key 'gtp_conversion_uploaded' not exists.</li>
  </ul>
  
  <p>I tried it with a LEFT JOIN, but the problem is that if the meta_value of meta_key 'gtp_conversion_uploaded' is equal to 1, I still get results.</p>