Question 6144 – Operating-Systems
May 16, 2024Question 5318 – UGC NET CS 2013 Dec-paper-2
May 16, 2024ER-Model
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Question 9
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What is the optimized version of the relation algebra expression πA1(πA2(σF1(σF2(r)))), where A1, A2 are sets of attributes in with A1 ⊂ A2 and F1, F2 are Boolean expressions based on the attributes in r?
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πA1 (σ(F1∧F2) (r))
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πA1 (σ(F1∨F2) (r))
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πA2 (σ(F1∧F2) (r))
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πA2 (σ(F1∨F2) (r))
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Question 9 Explanation:
Since A1 ⊂ A2 will get only attribute A1 as it is in the outside. So we can remove project A2.
Two Selects with Boolean expression can be combined into one select with AND of two Boolean expressions.
Two Selects with Boolean expression can be combined into one select with AND of two Boolean expressions.
Correct Answer: A
Question 9 Explanation:
Since A1 ⊂ A2 will get only attribute A1 as it is in the outside. So we can remove project A2.
Two Selects with Boolean expression can be combined into one select with AND of two Boolean expressions.
Two Selects with Boolean expression can be combined into one select with AND of two Boolean expressions.