GATE CS 2014 Set 3 — Question 31
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Databases → Relational Model → Query Optimization
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Question
What is the optimized version of the relation algebra expression , where are sets of attributes in with and are Boolean expressions based on the attributes in ?
Correct answer
(A) π_(A1)(σ_((F1 ∧ F2))(r))
Solution
The expression is .
1.Selection Optimization: A sequence of selection operations is equivalent to a single selection with the conjunction (AND) of the predicates. Therefore, .
2.Projection Optimization: A sequence of projection operations where is equivalent to simply , because the outer projection restricts the attributes further to , which are already present in .
Combining these, the optimized expression is .Continue learning with Success Tracker
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