Query to find all bars that sell three different beers at the same price

Question

Query to find "All bars that sell three different beers at the same price?"

My Tables are

Sells(bar,beer,price) - bar - foreign Key.. Bars(name,addr) - name primary key.

I thought of something like this but that dosent seem to work ...

 Select A.bar As bar , B.bar as bar  
 From Sells AS A, Sells AS B 
 Where A.bar = B.bar and A.beer <> B.beer  
 Group By(A.beer) 
 Having Count(Distinct A.beer) >= 2

Is this the correct SQL query ?

Answer 1

I would do it this way:

Select A.bar
From Sells AS A
JOIN Sells AS B ON (A.bar = B.bar AND A.price = B.price 
    AND A.beer <> B.beer)
JOIN Sells AS C ON (A.bar = C.bar AND A.price = C.price 
    AND A.beer <> C.beer AND B.beer <> C.beer)

In MySQL in particular, the join solution is likely to be more efficient than GROUP BY.

Answer 2

Select ...
From Bars As B
Where Exists    (
                Select 1
                From Sells As S1
                Where Exists    (
                                Select 1
                                From Sells As S2
                                Where S2.bar = S1.bar
                                    And S2.beer <> S1.beer
                                    And S2.price = S1.price
                                )
                    And S1.Bar = B.name
                Having Count(*) = 3     
                )