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Exercise 5.5 Consider the instance of the Sailors relation shown in Figure 5.1. 1. Write SQL queries to compute the average rating, using AVG; the sum of the ratings, using SUM; and the number of ratings, using COUNT. 2. If you divide the sum just computed by the count, would the result be the same as the average? How would your answer change if these steps were carried out with respect to the age field instead of rating? 3. Consider the following query: Find the names of sailors with a higher rating than all sailors with age < 21. The following two SQL queries attempt to obtain the answer to this question. Do they both compute the result? If not, explain why. Under what conditions would they compute the same result? SELECT S.sname FROM Sailors S WHERE NOT EXISTS ( SELECT * FROM Sailors S2 WHERE S2.age < 21 AND S.rating <= S2.rating)

Exercise 5.5 Consider the instance of the Sailors relation shown in Figure 5.1. 1. Write SQL queries to compute the average rating, using AVG; the sum of the ratings, using SUM; and the number of ratings, using COUNT. 2. If you divide the sum just computed by the count, would the result be the same as the average? How would your answer change if these steps were carried out with respect to the age field instead of rating? 3. Consider the following query: Find the names of sailors with a higher rating than all sailors with age < 21. The following two SQL queries attempt to obtain the answer to this question. Do they both compute the result? If not, explain why. Under what conditions would they compute the same result? SELECT S.sname FROM Sailors S WHERE NOT EXISTS ( SELECT * FROM Sailors S2 WHERE S2.age < 21 AND S.rating <= S2.rating)

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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Exercise 5.5 Consider the instance of the Sailors relation shown in Figure 5.1. 1. Write SQL queries to compute the average rating, using AVG; the sum of the ratings, using SUM; and the number of ratings, using COUNT. 2. If you divide the sum just computed by the count, would the result be the same as the average? How would your answer change if these steps were carried out with respect to the age field instead of rating? 3. Consider the following query: Find the names of sailors with a higher rating than all sailors with age < 21. The following two SQL queries attempt to obtain the answer to this question. Do they both compute the result? If not, explain why. Under what conditions would they compute the same result? SELECT S.sname FROM Sailors S WHERE NOT EXISTS SELECT FROM Sailors S2 WHERE S2.age < 21 AND S.rating <= S2.rating )
Transcribed Image Text:Exercise 5.5 Consider the instance of the Sailors relation shown in Figure 5.1. 1. Write SQL queries to compute the average rating, using AVG; the sum of the ratings, using SUM; and the number of ratings, using COUNT. 2. If you divide the sum just computed by the count, would the result be the same as the average? How would your answer change if these steps were carried out with respect to the age field instead of rating? 3. Consider the following query: Find the names of sailors with a higher rating than all sailors with age < 21. The following two SQL queries attempt to obtain the answer to this question. Do they both compute the result? If not, explain why. Under what conditions would they compute the same result? SELECT S.sname FROM Sailors S WHERE NOT EXISTS SELECT FROM Sailors S2 WHERE S2.age < 21 AND S.rating <= S2.rating )
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