1 Relational Algebra & SQL Query Formulation Exercise

2 Exercise 4: Relational Algebra and SQL Given relational schema: Frequent (D, P) Serves (P, B) Likes (D, B) Attributes: P (pub), B (beer), D (drinker) 1) The pubs that serve a beer that Jefferson likes. 2) Drinkers that frequent at least one pub that serves “Bud” or “Becks”. 3) Drinkers that frequent only pubs that serve some beer they like 4) Drinkers that frequent only pubs that serve no beer they like.

3 1) Algebra  Solution 1:  Solution 2:  Solution 3:  Solution 4:

4 2) SQL  Solution 1 :  Solution 2: SELECT p FROM S, L WHERE S.b=L.b AND L.d=‘Jefferson’ SELECT d FROM F WHERE F.p in ( SELECT p FROM S WHERE b IN (‘Bud”, ‘Becks’))

5 2) SQL  Solution 3 : SELECT d FROM F EXCEPT SELECT d FROM ( SELECT * FROM F EXCEPT SELECT d,p FROM S, L WHERE S.b = L.b)

6 2) SQL  Solution 4 : SELECT d FROM F EXCEPT SELECT d FROM ( SELECT * FROM F INTERSECT SELECT d,p FROM S, L WHERE S.b = L.b)

7 2) SQL  Solution 4 (alternative solution) : SELECT d FROM F WHERE ( SELECT COUNT (DISTINCT p) FROM S, L WHERE F.p=S.p AND S.b=L.b AND L.d=F.d) = 0