BUG #17408: Duplicate aliases silently fail

The following bug has been logged on the website:

Bug reference:      17408
Logged by:          Kevin Potgieter
Email address:      porturpotgieter@gmail.com
PostgreSQL version: 13.6
Operating system:   Not related
Description:

Hi,

Assigning aliases to columns works perfectly.

eg. "SELECT name AS customer_name FROM customers"

However you are able to assign duplicate aliases which does not cause a
conflict

eg. "SELECT name AS customer_name, surname AS customer_name FROM
customers"

The expectation here is that duplicate aliases would cause the query to fail
due to duplicate column names in the result, however there is no error or
warning.

Regards
Kevin