The psql interactive terminal does not have a built-in way of clearing the
screen. What I usually do if I really need the screen cleared is quit, run
clear from the shell, and then open a new psql session. This is
unnecessary though. Instead, we can use the \! command to execute a shell
command, in this case, the clear command.
> \! clear
This clears the screen in one step and keeps our current session running.
See the psql docs for more details.