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Relational Algebra and SQL

Relational Algebra and SQL. Given relational schema: Frequent ( D, P ) Serves ( P, B ) Likes ( D, B ) Attributes: P (pub), B (beer), D (drinker) The pubs that serve a beer that Jefferson likes. Drinkers that frequent at least one pub that serves “Bud” or “Becks”.

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Relational Algebra and SQL

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

  2. 1) Algebra • Solution 1: • Solution 2: • Solution 3: • Solution 4:

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

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

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

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