title: How to use sql query in sql functions
body: <p>There is table like below</p>
  
  <pre><code>---------------------------------------------------------------
  title(varchar)  |  date(datetime)       |  id(int, primary key)
  ---------------------------------------------------------------
  title1          |  2015-07-24 01:19:48  |  1
  title2          |  2015-07-25 07:19:23  |  2
  title3          |  2015-07-26 23:19:18  |  3
  title4          |  2015-07-27 11:19:45  |  4
  title5          |  2015-07-30 02:19:40  |  5
  </code></pre>
  
  <p>Since the date value is saved as <a href="https://en.wikipedia.org/wiki/Greenwich_Mean_Time" rel="nofollow">GMT</a>,  I have to convert it to local time zone.(In my case it's GMT+9)</p>
  
  <p>I tried </p>
  
  <pre><code>SELECT convert_tz(date, '+00:00', '+09:00') 
  FROM 
  my_table
  </code></pre>
  
  <p>but doesn't work.</p>
  
  <p>How can I select rows with converted time values? Is it proper to use sub query in my case?</p>
  
  <p>What I want to get is like below...</p>
  
  <pre><code>2015-07-24 10:19:48
  2015-07-25 16:19:23
  2015-07-27 08:19:18
  2015-07-27 20:19:45
  2015-07-30 10:19:40
  </code></pre>