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31

DBMS Korth Edition 6 Exercise 6 Question 19 (Page No. 254)
Give a tuple-relational-calculus expression to find the maximum value in relation r (A).

ajaysoni1924 asked in Databases Mar 26, 2019

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32

DBMS Korth Edition 6 Exercise 6 Question 15 (Page No. 253-254)
Consider the employee database shown here. Give expressions in tuple relational calculus and domain relational calculus for each of the following queries: a. Find the names of all employees who work for First Bank Corporation . b ... (person name, company name, salary) company (company name, city) manages (person name, manager name)

ajaysoni1924 asked in Databases Mar 26, 2019

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33

DBMS Korth Edition 6 Exercise 6 Question 14 (Page No. 253)
Consider the following relational schema for a library: member(memb_no, name, dob) books(isbn, title, authors, publisher) borrowed(memb_no, isbn, date) Write the following queries in relational algebra. a. Find the names of members ... if a member does not borrow any books, then that member does not appear in the borrowed relation at all.

ajaysoni1924 asked in Databases Mar 26, 2019

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34

DBMS Korth Edition 6 Exercise 6 Question 13 (Page No. 253)
Consider the relational database shown here. Give a relational-algebra expression for each of the following queries: a. Find the company with the most employees. b. Find the company with the smallest payroll. c. Find those ... works (person name, company name, salary) company (company name, city) manages (person name, manager name)

ajaysoni1924 asked in Databases Mar 26, 2019

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35

DBMS Korth Edition 6 Exercise 6 Question 12 (Page No. 253)
Using the university example, write relational-algebra queries to find the course sections taught by more than one instructor in the following ways: a. Using an aggregate function. b. Without using any aggregate functions.

ajaysoni1924 asked in Databases Mar 26, 2019

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36

DBMS Korth Edition 6 Exercise 6 Question 11 (Page No. 252)
Consider the relational database shown here, where the primary keys are underlined. Give an expression in the relational algebra to express each of the following queries: a. Find the names of all employees who work for First Bank ... works (person name, company name, salary) company (company name, city) manages (person name, manager name)

ajaysoni1924 asked in Databases Mar 26, 2019

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37

DBMS Korth Edition 6 Exercise 6 Question 10 (Page No. 252)
Write the following queries in relational algebra, using the university schema. a. Find the names of all students who have taken at least one Comp. Sci. course. b. Find the IDs and names of all students who have ... instructor. d. Find the lowest, across all departments, of the per-department maximum salary computed by the preceding query.

ajaysoni1924 asked in Databases Mar 26, 2019

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38

DBMS Korth Edition 6 Exercise 6 Question 9 (Page No. 252)
Describe how to translate join expressions in SQL to relational algebra.

ajaysoni1924 asked in Databases Mar 26, 2019

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39

DBMS Korth Edition 6 Exercise 6 Question 8 (Page No. 251)
Consider the relational database given below where the primary keys are underlined. Give an expression in tuple relational calculus for each of the following queries: a. Find all employees who work directly for Jones. b. Find all ... works (person name, company name, salary) company (company name, city) manages (person name, manager name)

ajaysoni1924 asked in Databases Mar 26, 2019

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40

DBMS Korth Edition 6 Exercise 6 Question 7 (Page No. 251)
Let R = (A, B) and S = (A,C), and let r (R) and s(S) be relations.Write expressions in relational algebra for each of the following queries: a. {< a > | ∃ b (< a, b > ∈ r ∧ b = 7)} b. {< a, b, c > | < a, b > ∈ r ∧ < ... | ∃ c (< a, c > ∈ s ∧ ∃ b1, b2 (< a, b1 > ∈ r ∧ < c, b2 > ∈ r ∧ b1 > b2))}

ajaysoni1924 asked in Databases Mar 26, 2019

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41

DBMS Korth Edition 6 Exercise 6 Question 6 (Page No. 251)
Let R = (A, B, C), and let r1 and r2 both be relations on schema R. Give an expression in the domain relational calculus that is equivalent to each of the following: a. $\prod _A(r1)$ b. $\sigma _{B =17} (r1)$ c. r1 ∪ r2 d. r1 ∩ r2 e. r1 − r2 f. $\prod _{A,B}(r1) \Join \prod _{B,C}(r2)$

ajaysoni1924 asked in Databases Mar 26, 2019

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42

DBMS Korth Edition 6 Exercise 6 Question 5 (Page No. 251)
Let the following relation schemas be given: R = (A, B,C) S = (D, E, F) Let relations r(R) and s(S) be given. Give an expression in the tuple relational calculus that is equivalent to each of the following: a. $\prod _A(r)$ b. $\sigma _{B =17} (r )$ c. r × s d. $\prod _{A,F} (\sigma _{C = D}(r × s))$

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43

DBMS Korth Edition 6 Exercise 6 Question 4 (Page No. 250)
(Division operation): The division operator of relational algebra, , is defined as follows. Let r (R) and s(S) be relations, and let S ⊆ R; that is, every attribute of schema S is also in schema R. ... using division. (By doing so, you would have shown how to define the division operation using the other relational algebra operations.)

ajaysoni1924 asked in Databases Mar 26, 2019

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44

DBMS Korth Edition 6 Exercise 6 Question 3 (Page No. 250)
The natural outer-join operations extend the natural-join operation so that tuples from the participating relations are not lost in the result of the join. Describe how the theta-join operation can be extended so that tuples from the left, right, or both relations are not lost from the result of a theta join.

ajaysoni1924 asked in Databases Mar 26, 2019

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45

DBMS Korth Edition 6 Exercise 6 Question 2 (Page No. 250)
Consider the relational database given below, where the primary keys are underlined. Give an expression in the relational algebra to express each of the following queries: a. Find the names of all employees who live in the same ... works (person name, company name, salary) company (company name, city) manages (person name, manager name)

ajaysoni1924 asked in Databases Mar 26, 2019

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46

DBMS Korth Edition 6 Exercise 6 Question 1 (Page No. 249)
Write the following queries in relational algebra, using the university schema. a. Find the titles of courses in the Comp. Sci. department that have 3 credits. b. Find the IDs of all students who were taught by an ... enrollment, across all sections, in Autumn 2009. g. Find the sections that had the maximum enrollment in Autumn 2009.

ajaysoni1924 asked in Databases Mar 26, 2019

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47

DBMS Korth Edition 6 Exercise 4 Question 17 (Page No. 155)
Explain why, when a manager, say Satoshi, grants an authorization, the grant should be done by the manager role, rather than by the user Satoshi.

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48

DBMS Korth Edition 6 Exercise 4 Question 16 (Page No. 155)
Referential-integrity constraints as defined generally involve exactly two relations. Consider a database that includes the relations shown below . Suppose that we wish to require that every name that appears in address appears in either ... (name, office, phone, salary) hourly worker (name, hourly wage) address (name, street, city)

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49

DBMS Korth Edition 6 Exercise 4 Question 14 (Page No. 155)
Show how to define a view tot credits (year, num credits), giving the total number of credits taken by students in each year.

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50

DBMS Korth Edition 6 Exercise 4 Question 13 (Page No. 155)
Under what circumstances would the query select * from student natural full outer join takes natural full outer join course include tuples with null values for the title attribute?

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51

DBMS Korth Edition 6 Exercise 4 Question 12 (Page No. 155)
For the database shown below, write a query to find those employees with no manager. Note that an employee may simply have no manager listed or may have a null manager. Write your query using an outer join and then write ... city) works (employee name, company name, salary) company (company name, city) manages (employee name, manager name)

ajaysoni1924 asked in Databases Mar 26, 2019

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52

DBMS Korth Edition 6 Exercise 4 Question 10 (Page No. 154)
SQL provides an n-ary operation called coalesce, which is defined as follows: coalesce(A1, A2, . . . , An) returns the first non null Ai in the list A1, A2, . . . , An, and returns null if all of A1, A2, . . ... name and address, and that the solution is correct even if some tuples in a and b have null values for attributes name or address.

ajaysoni1924 asked in Databases Mar 26, 2019

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53

DBMS Korth Edition 6 Exercise 4 Question 9 (Page No. 154)
SQL allows a foreign-key dependency to refer to the same relation, as in the following example: create table manager (employee name varchar(20) not null manager name varchar(20) not null, primary key employee name, foreign ... every manager also be an employee. Explain exactly what happens when a tuple in the relation manager is deleted.

ajaysoni1924 asked in Databases Mar 26, 2019

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54

DBMS Korth Edition 6 Exercise 4 Question 8 (Page No. 154)
we expect the constraint “an instructor cannot teach sections in two different classrooms in a semester in the same time slot” to hold. a. Write an SQL query that returns all (instructor, section) combinations that violate this constraint. b. Write an SQL assertion to enforce this constraint.

ajaysoni1924 asked in Databases Mar 26, 2019

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55

DBMS Korth Edition 6 Exercise 4 Question 7 (Page No. 154)
Consider the relational database shown below. Give an SQL DDL definition of this database. Identify referential-integrity constraints that should hold, and include them in the DDL definition. employee (employee name, street, city) works (employee name, company name, salary) company (company name, city) manages (employee name, manager name)

ajaysoni1924 asked in Databases Mar 26, 2019

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56

DBMS Korth Edition 6 Exercise 4 Question 6 (Page No. 153)
Complete the SQL DDL definition of the university database shown below in figure 4.8 to include the relations student, takes, advisor, and prereq.

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57

DBMS Korth Edition 6 Exercise 4 Question 5 (Page No. 153)
Show how to define the view student_grades (ID, GPA) giving the gradepoint average of each student, based on the query given below 3.2; recall that we used a relation grade_points(grade, points) to get the numeric ... Make sure your view definition correctly handles the case of null values for the grade attribute of the takes relation.

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58

DBMS Korth Edition 6 Exercise 4 Question 3 (Page No. 153)
Suppose we have three relations r (A, B), s(B, C), and t(B, D), with all attributes declared as not null. Consider the expressions r natural left outer join (s natural left outer join t), and (r natural left outer ... Is the above pattern, with C null and D not null possible in the result of the first expression? Explain why or why not.

ajaysoni1924 asked in Databases Mar 26, 2019

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59

DBMS Korth Edition 6 Exercise 4 Question 2 (Page No. 152)
Outer join expressions can be computed in SQL without using the SQL outer join operation. To illustrate this fact, show how to rewrite each of the following SQL queries without using the outer join expression. a. select* from student natural left outer join takes b. select* from student natural full outer join takes

ajaysoni1924 asked in Databases Mar 26, 2019

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60

DBMS Korth Edition 6 Exercise 4 Question 1 (Page No. 152)
Write the following queries in SQL: a. Display a list of all instructors, showing their ID, name, and the number of sections that they have taught. Make sure to show the number of sections as 0 for ... of instructors in each department, without using scalar sub queries. Make sure to correctly handle departments with no instructors.

ajaysoni1924 asked in Databases Mar 26, 2019

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