title: Event scheduler MySql without expired time
body: <p>I read article about the event scheduler on MySql.Then I got this structure,</p>
  
  <pre><code>CREATE
  [DEFINER = { user | CURRENT_USER }]
  EVENT
  [IF NOT EXISTS]
  event_name
  ON SCHEDULE schedule
  [ON COMPLETION [NOT] PRESERVE]
  [ENABLE | DISABLE | DISABLE ON SLAVE]
  [COMMENT 'comment']
  DO event_body;
  </code></pre>
  
  <p>I got some interested thing to know about it, 
  1. Could this event schedule havent expired time?
  2. What is the ENABLE | DISABLE | DISABLE ON SLAVE mean?</p>
  
  <p>Any respon will be appreciate,Thx.</p>