9. PC(model, speed, price) is a relation. Which relational algebra expression an
ID: 3585770 • Letter: 9
Question
9. PC(model, speed, price) is a relation. Which relational algebra expression answers the query "What PC models have a speed higher than 3"? speed-3 (model (PC) ) model (speed-3 (PC)) model (Ogpeed-3 (PC)) speed-3 (Omodel (PC)) C. b. d. 10. R(A, B, C, D) has functional dependencies AB->C and CD->A. Which of the following is a key? a. AB b. CD C. ABC d. BCD 11. A BCNF decomposition of the relation in Problem 10 is ABC and ACD ABC and ABD c. ABC and BCD d. AB and CD a. b. 12. A 3NF decomposition of the relation in Problem 10 is ABC and ACD AB and CD AB, CD, and ABD ABC, ACD, and ABD a. C. b. d. 13. The closure of CD in the relation in Problem 10 is a. CD b. ACD C. BCD d. ABCD 14. R(A, B, C, D) has FD's C->A and C->B. A BCNF decomposition is AB and BCD ABC and CD C. AC and BCD d. ABD and BC. a. b.Explanation / Answer
Q.PC(model, speed, price) is a relation. Which relational lgebra expression answers the query " What PC models have a speed higher than 3".
Answer: (a) speed>3(model(PC))
(Select operator): this is used to select the speed that is greater than 3 in the table PC.
(projection operator): It is used to project the column from the table PC. In this case it will project the model column from the PC table then after the select operator will select the model who have speed greater than 3.
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