Hiding results using :post

[Roger Mason]

Hello,

I'd like to be able to hide results, for example when I expect the
them to span many lines.  I know I can hit =tab= on the #+RESULTS: line,
but I'd like to be able to set this automatically.

My most recent effort:

#+name: hideresults
#+begin_src emacs-lisp :results none :exports none
(add-to-invisibility-spec '(org-babel-hide-result . t))
#+end_src

run like this

#+header: :engine postgresql :dbhost "localhost"  :dbuser "rmason" :database 
"test" :colnames yes
#+header: :post hideresults
#+name: pgquery
#+begin_src sql
select timestamp,nempty0 from settings where timestamp like '%20210528%'
#+end_src

produces

#+RESULTS: pgquery
: nil

I'm sure there is a way to do this, but I need some pointers as to how.

Thanks for any help.

Roger

Org mode version 9.2.3 (release_9.2.3-390-gfb5091 @
/home/rmason/.emacs.d/org-git/lisp/)

GNU Emacs 27.2 (build 1, amd64-portbld-freebsd11.4, X toolkit, cairo version 
1.16.0, Xaw3d scroll bars)