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Unit 2: Relational Query Languages

20232m

A row from a table is selected by

  • (i) selection operator
  • (ii) projection operator
  • (iii) union operator
  • (iv) none of these
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Answer: (i) selection operator

Explanation: In relational algebra, selection (sigma) selects rows/tuples satisfying a condition horizontally. Projection (pi) selects columns/attributes vertically. Union combines tuples from two compatible relations. So row selection is via selection operator, e.g., sigma_{age>20}(Student).

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