Musicals where 1 song is a medley of songs from other musicals?

That may be the only medley I can think of from a legitimate musical but other show tunes have been referenced in other musicals. For example, listen to Shaw from The Frogs and you'll hear Sondheim play on You Did It from My Fair Lady. Mel Brooks also makes musical jokes in The Producers such as the phrase "Tony, Tony" borrowed from West Side Story.

Reviews such as Forbidden Broadway have mashed together multiple songs into one number.