title: How to group/select JSON type column (PG::UndefinedFunction: ERROR: could not identify an equality operator for type json)
body: <p>I wanna do</p>
  
  <pre><code>&lt;MODEL&gt;.select("brief_content").group("brief_content")
  </code></pre>
  
  <p>Here's the table scheme ,</p>
  
  <pre><code>                :id =&gt; :integer,
             :content =&gt; :json,
       :brief_content =&gt; :json
  </code></pre>
  
  <p>But I got the errors,</p>
  
  <p>How can I do, Thanks</p>
  
  <pre><code>companyAlarmLog Load (0.9ms)  SELECT company_alarm_logs.id, company_alarm_logs.name, company_alarm_logs.utc_time, company_alarm_logs.company_alarm_test_id, company_alarm_logs.brief_content, brief_content FROM "company_alarm_logs" GROUP BY brief_content ORDER BY utc_time
  E, [2014-06-24T09:40:39.069988 #954] ERROR -- : PG::UndefinedFunction: ERROR:  could not identify an equality operator for type json
  LINE 1: ...t, brief_content FROM "company_alarm_logs"  GROUP BY brief_cont...
                                                               ^
  : SELECT company_alarm_logs.id, company_alarm_logs.name, company_alarm_logs.utc_time, company_alarm_logs.company_alarm_test_id, company_alarm_logs.brief_content, brief_content FROM "company_alarm_logs"  GROUP BY brief_content  ORDER BY utc_time
  Hirb Error: PG::UndefinedFunction: ERROR:  could not identify an equality operator for type json
  LINE 1: ...t, brief_content FROM "company_alarm_logs"  GROUP BY brief_cont...
  </code></pre>