title: how can i get Max value of a column in GreenDAO using QueryBuilder?
body: <p>I'm still rusty when it comes to ORM's, but i really love GREENDAO, for its extreme simplicity and speed.
  Can i please know how to get the Max value of a column in my table in GreenDao.
  Say i have a table with id and post id, and i want to get the highest value of post id?
  I've tried using the raw sql builder, but no way</p>
  
  <pre><code>public void getMaxId(int postId)
     {
         return postsDao.queryBuilder().where(new WhereCondition.StringCondition(SELECT MAX(PostId) FROM POSTS).build());
     }
  </code></pre>
  
  <p>Thanks</p>