title: MySQL: Return 2 different result together
body: <p>My SQL statement looks like that</p>
  <pre><code>SELECT qe.id, qe.content, a.id, a.content, a.addDT, acr.checked, acr.score  
  FROM `questions_and_exercises` qe, 
  `questions from-to` qft 
  LEFT JOIN `questions-answers` qa ON (qa.qid=qe.id AND qa.uid=qft.uid) 
  LEFT JOIN answers a ON (a.id=qa.aid) 
  LEFT JOIN `answer_chk_results` acr ON (acr.aid=a.id)
  AND qft.to_lid=2 
  WHERE qft.to_uid=3 
  </code></pre>
  <p>Now, <code>WHERE</code>part is not doing what I want. Trying to achieve this result:</p>
  <ul>
  <li>Select all where qft.to_lid=? (it means qft.to_uid=NULL) <strong>(ALWAYS)</strong></li>
  <li>If there are rows where qft.to_uid=? (it means qft.to_lid=NULL) select them too (ONLY IF THERE ARE SUCH ROWS). In other words append to result.</li>
  </ul>
  <p>Is there anyway to achieve this byu only one sql statement?</p>
  <h1>update</h1>
  <p><img src="https://i.stack.imgur.com/VUhMC.png" alt="enter image description here" /></p>
  <p>For ex when I query</p>
  <pre><code>WHERE qft.to_lid=2 AND qft.to_uid=NULL
  WHERE qft.to_uid=2 AND qft.to_lid=NULL
  </code></pre>
  <p>I want to get rows with ids: 4,5,6 . If one of this where conditions has no result show other one. In other words this conditions has no relationship between each other</p>