Auxiliary-Statements.md

+Provides a way to write auxiliary statements for use in a larger query. It's reconfigured on the model, and then can be used during querying process. [PostgreSQL Docs](https://www.postgresql.org/docs/9.1/static/queries-with.html)
+
+# How it works
+
+### Model
+
+First you need to configure the statements that you want to use. These statements are very similar to scopes, but with a little more options:
+```ruby
+# models/user.rb
+class User < ActiveRecord::Base
+
+  auxiliary_statement :last_comment do |cte|
+    cte.query Comment.distinct_on(:user_id).order(:user_id, id: :desc)
+    cte.attributes content: :last_comment_content
+  end
+
+end
+```
+
+The statement is lazy load, so the block is called only when a query requires its usage. To configure your statement, those are the options available:
+
+`cte.query` The query that will be performed inside the auxiliary statement (WITH). It most likely to be queries that brings extra information related to the main class, in this case the `User` class.
+
+`cte.attributes` The list of attributes that will be exposed to the main query and after be able to access through the entries fetch. It's read as `The column form the query => The alias exposed`. It accepts join columns in the left side as `'table.column' => 'alias'`.
+
+`cte.join_type` The type of join between the main query and statement query. By default it's set to `:inner`, that will perform an `INNER JOIN`. The options are `:inner, :left, :right, :full`.
+
+`cte.join` The columns to be used on the join in the main query. It has similar behavior as the attributes, and it's read as `The column from the main query == The column from the statement query`. It accepts join columns in both sides as `'table.column' => 'table.column'`.
+
+### Querying
+```ruby
+with(*list)
+```
+
+Once you have configured all your statements, you can easily use them by calling `with` method.
+```ruby
+user = User.with(:last_comment, :first_comment).first
+user.last_comment_content
+```
+
+You are able to use all the exposed columns set on the right side of the `attributes` configuration in other methods like `where`, `order`, `group`, etc.
+```ruby
+user = User.with(:last_comment).order(:last_comment_content)
+```
\ No newline at end of file