That's the thing - it's a tag, not a song. It can be added to any number of songs, like the tags at the end of Does Your Chewing Gum Lose Its Flavor:

On the bedpost over...
Y'know that I love and I wanna hold you tight
Monday, Tuesday, Wednesday, Thursday, Friday, Saturday night.

On the bedpost over...
A dollar is a dollar and a dime is a dime.
I'd sing another chorus but I haven't got the time.

On the bedpost over - night.