Canonical url for latest document set?

Hi,

There was a suggestion a few years ago on this forum about adding a
canonical url to the documentation set:
https://www.postgresql.org/message-id/04E4F5A6-6526-4DDC-A9E5-2991E3B2ED83%40cantoute.com

Was there a reason for not doing this? At the moment it can be pretty
annoying googling something like "postgres select syntax", and getting a
pretty random selection of duplicate pages, none of which matches the
current version of Postgres. Even google for "postgres 9.6 select syntax"
still doesn't return the correct version for me.

In contrast, other documentation sites such as MySql, CouchDb, Python,
Django, etc. all behave much better in search engine results. For CouchDb
and Django you can see use of the canonical tag on the documentation
pages. For the others they must be doing something different, but still
they've managed to direct Google to the single, current version of the
correct page.

I'm just wondering if something has looked into this already, or if
canonical url is something that could be tested for the postgres
documentation?

Here is some information from google:
https://webmasters.googleblog.com/2009/02/specify-your-canonical.html

The goal for me would be to make the documentation for the current version
of Postgres rise to the top of search engine results, and to remove the
random results for older versions.

What do you think?

Kind regards,

Conor McNally