Gate2018 cs Q52

0. Consider the relations r(A, B) and s(B, C), where s.B is a primary key and r.B is a foreign key referencing s.B. Consider the query Q: r⋈(σB<5(s)) Let LOJ denote the natural left outer-join operation. Assume that r and s contain no null values.

  • Option : C
  • Explanation :

    Given query: r ⋈ ( σB<5(s))
    ABC
    a12c1
    a24c1
    a34c1

    A: σB<5(r ⋈ s)
    ABC
    a12c1
    a24c1
    a34c1

    B:  σB<5(r ⋈ s)
    ABC
    a12c1
    a24c1
    a34c1

    C: r ⋈ (σB<5(s))
    ABC
    a12c1
    a24c1
    a34c1
    a46Null
    a56Null

    D: σ;B<5 (r) ⋈  s
    ABC
    a12c1
    a24c1
    a34c1

    Option “C” query result not equal to given query.
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