Order function in select clause

This feature allows user to use the distance value as a part of a calculation of a new column in the select clause. The motivation of this feature lies in the fact that Postgres does not allow transient column to be used as a part of `ORDER BY` calculation clause. To make this clearer, you can try running the following SQL using MySQL and then using Postgres.

http://sqlfiddle.com/#!1/3e61c/1

With Postgres, the above SQL will produce an error because we are using a function of transient column in the `ORDER BY` clause.