Can anyone tell why 1st is not correct?
My approach:-When we will join drinker and bar,we will get tuples of the drinker and the bar corresponding to his/her city.One tuple per drinker will come.Then we will join this with frequent ,the key will be (DrinkerName,BarName),As from previous query we have one tuple,so that will be matched at max. one tuple only.And we project drinker's name.
What did i miss?