I wanted to add a timestamp to my MySQL command prompt to keep a track of when the previous command on my screen was executed (my mysql window is open all the time). As per MySQL's docs, this can be done with something like:
mysql> prompt [\w, \R:\m]>
PROMPT set to '[\w, \R:\m]> '
(Note that there's a space after the > in the prompt command.)
The other options for the prompt command are: