title: MySQL Select response missing rows with NULL values when <> used
body: <p>I am not getting what I need to get from a MySQL select query.  The response is missing all rows that have an attribute 'c2' that is NULL when I add a clause 'c2 &lt;> 'A'.  I want those rows as well.  How can I change the query (Q2) to do this?</p>
  
  <p>Here's the code that reproduces my issue. </p>
  
  <pre><code>CREATE  TABLE T (
  `C1` VARCHAR(63) NOT NULL ,
  `C2` VARCHAR(31) NULL);
  
  INSERT INTO T VALUES ('Mike', 'A');
  INSERT INTO T VALUES ('Mike', 'B');
  INSERT INTO T VALUES ('Mike', 'C');
  INSERT INTO T VALUES ('Mike', NULL);
  INSERT INTO T VALUES ('Mark', 'C');
  INSERT INTO T VALUES ('Mark', NULL);
  </code></pre>
  
  <h1>Q1:</h1>
  
  <pre><code>SELECT * FROM T WHERE C1 = 'Mike';
  </code></pre>
  
  <p>Returned values are as I expected:</p>
  
  <ul>
  <li>'Mike', 'A'</li>
  <li>'Mike', 'B'</li>
  <li>'Mike', 'C'</li>
  <li>'Mike', NULL</li>
  </ul>
  
  <h1>Q2:</h1>
  
  <pre><code>SELECT * FROM T WHERE C1 = 'Mike' AND C2 &lt;&gt; 'A';
  </code></pre>
  
  <p>Returned values are NOT as I expected:
   - 'Mike', 'B'
   - 'Mike', 'C'</p>
  
  <h1>MISSING: ('Mike', NULL)</h1>