minor review comment

This module needs a readme file describing the functionality of the module. 

Other than that I only have one small comment 
Not all db query functions can be chained: 

* join returns table alias for the join - https://api.drupal.org/api/drupal/includes!database!select.inc/function/SelectQuery%3A%3Ajoin/7
* addField also returns alias for the field  - https://api.drupal.org/api/drupal/includes!database!select.inc/function/SelectQuery%3A%3AaddField/7

So the only solution here is to mix chaining and no-chaining...