Avoid to create a new window in sql mode

Question

I use a monitor and a laptop screen as my multimonitor setup.

Unfortunately the monitor and the laptop differs in resolution. So I use 2 frames, one frame on the monitor and one frame on the laptop screen.

Both frames are connected to one Emacs instance.

MONITOR: I will call the frame that's opened on monitor as frame 1. In the frame 1 on the monitor, I have a buffer opened with the default SQL-mode that's shipped with Emacs.

LAPTOP: On the laptop screen, there is a SQL-process being displayed in the Emacs frame 2.

SITUATION: In the frame 1, in the buffer with SQL-mode, I call M-x sql-send-region to send a SQL-statement to the SQL-process.

I see the result on the laptop screen in frame 2. But in the meanwhile, the SQL-mode propably have detected there is no window in the Emacs frame 1, so Emacs opens a new window with the same buffer of the SQL-process.

As the result, there are two windows on two screens, viewing the same buffer (the SQL-process).

I would prevent that the SQL-mode opens a new window when sending a SQL-statement to the SQL-process. How could I 'tell' Emacs to prevent that?

EDIT as answered below, this question is solved by now. See the second option from the user bmag.

Answer 1

IIUC, the problem is that Emacs doesn't reuse the window from frame 2 when frame 1 is the selected frame. As per Window-Choice page in the manual, you can set pop-up-frames to t:

(setq pop-up-frames t)

Setting pop-up-frames to t will make Emacs consider windows on other frames whenever it needs to display a buffer. If you want Emacs to reuse windows from another frame only for SQL's process buffer, you need to add an entry to display-buffer-alist:

(push '("<buffer-name>" nil . ((reusable-frames . t))) display-buffer-alist)

Where <buffer-name> should be replaced with the name of SQL's process buffer. The documentation of display-buffer-alist and display-buffer (via C-h v and C-h f) explains them in great detail. You can read related pages from the Elisp manual to learn more.

Note that I am assuming sql-mode uses pop-to-buffer or similar to switch to SQL's process buffer. If it uses switch-to-buffer or split-window (it shouldn't), then my answer isn't likely to work.

Answer 2

Untested, as I don't use sql-mode:

(defun nadvice/sql-send-string (old-fun &rest args)
  (cl-letf* (((old-display-buffer (symbol-function #'display-buffer))
              ((symbol-function #'display-buffer)
               (lambda (buffer-or-name &rest iargs)
                 (unless (get-buffer-window-list buffer-or-name)
                   (apply old-display-buffer buffer-or-name iargs))))))
    (apply old-fun args)))

(advice-add 'sql-send-string :around #'nadvice/sql-send-string)