This is doable with a hook and advice I think. The hook will hide the results if you use :results hide in the header.

I had to use the advice to remove the results before hand, so that you toggle the visibility off. This is pretty lightly tested. you could eliminate 

(defun hide-results (&optional &rest args)
  (let ((results (cdr (assoc :results (third (org-babel-get-src-block-info 'light))))))
    (when (string-match "hide" results)
      (org-babel-hide-result-toggle t))))

(add-hook 'org-babel-after-execute-hook 'hide-results)

(advice-add 'org-babel-execute-src-block :before (lambda (&rest args) (org-babel-remove-result)))

I guess there are other ways that might work too.

#+BEGIN_SRC jupyter-python :results hide
print(5)
#+END_SRC

#+RESULTS:
: 5

John

-----------------------------------
Professor John Kitchin (he/him/his)
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803

@johnkitchin
http://kitchingroup.cheme.cmu.edu

On Mon, Jun 7, 2021 at 10:03 AM Nick Savage <nick@nicksavage.ca> wrote:

My initial thoughts are that this is very possible. This might be an
area where we could add a new defcustom on always hiding the results to
allow the user to choose it. Without looking at the code, I think it
would be pretty straight forward to make an excursion to the results
line, toggle showing it, then going back to where the point was.

I can take a crack at a patch in the next day or so if no one else wants
to or gets there first.

On 6/7/21 8:51 AM, Roger Mason wrote:
> 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)
>