title: Hive query optimization for aggregated columns appear once in a select statement
body: <p>if there are multi aggregated column in one select, would the be evaluated only once? for example:</p>
  
  <pre><code>select
      date,
      count(userid) as uv,
      sum(isclick) as clickcnt,
      count(userid) / sum(isclick) as ctr
  from
      user_access_log
  group by
      1
  </code></pre>
  
  <p>here both <code>count(userid)</code> and <code>sum(isclick)</code>  are used twice, would they be evaluated twice or only once, will hive do any query optimization?</p>