title: MYSQL "not equal to" on enum
body: <p>I created a table with an enum column as follow</p>
  
  <pre><code>create table test_1(
      id BIGINT NOT NULL AUTO_INCREMENT,
      order_billing_status ENUM ("BILLING_IN_PROGRESS") DEFAULT NULL
  );
  </code></pre>
  
  <p>I insert two values as follow</p>
  
  <pre><code>+-----+----------------------+
  | id  | order_billing_status |
  +-----+----------------------+
  | 100 | NULL                 |
  | 200 | BILLING_IN_PROGRESS  |
  +-----+----------------------+
  </code></pre>
  
  <p>Now when I try to query like <code>select * from  test_1 where order_billing_status &lt;&gt; "BILLING_IN_PROGRESS";</code>, it is returning empty result, instead of returning the following.</p>
  
  <pre><code>+-----+----------------------+
  | id  | order_billing_status |
  +-----+----------------------+
  | 100 | NULL                 |
  +-----+----------------------+
  </code></pre>
  
  <p>Is this a bug in mysql or am I doing something wrong? If it's a bug, is there a work around or should I just use varchar instead of enum?</p>