'Need to know'- What was the beer did they drink on the set of Cheers? thanks

None, as it's illegal to drink while on set.

George Wendt (Norm) did not drink real beer while shooting Cheers. It was most likely carbonated iced tea.

A question I used to field occasionally was, “Are the actors on Cheers drinking real beer?” That was asked by people who were unfamiliar with how television shows are produced. They didn’t know that there are multiple “takes” of each scene; there would be slight variations from one take to the next. If an actor’s mug was supposed to be drained by the end of the scene, though, he would have to gulp down his drink every time, so that the footage would match with earlier takes. Had the actors — especially George Wendt (Norm) — been drinking real beer, they probably would have been sprawled out under the bar by the time the director called, “That’s a wrap.”

So, no: it may have looked like the real thing, but it was what used to be called Near Beer. It has virtually no alcohol in it — less than half of one percent.

http://tomreeder.wordpress.com/2009/10/01/fake-beer/

In the 1970s, there was a tv show here (Ireland) called "Hall's Pictorial Weekly", a satirical magazine show with news articles of interest interspersed with sketches and parodies. Many of the actors were well known comedians and theatrical personalities such as Eamon Morrissey and Frank Kelly (Father Jack in "Father Ted"), and one particular running sketch took place in a pub (naturally). Eamon Morrissey has stated that real beer was drank during filming and that many actors were, shall we say, the worse for wear by the end of the day.
https://en.wikipedia.org/wiki/Hall%27s_Pictorial_Weekly