程序代写代做代考 database ER SQL CS430/630 – Homework 3

CS430/630 – Homework 3

Released Mar 06, Due Mar 27

50 points (5/100 of final grade)

Instructions: The homework is due BEFORE CLASS on Tue Mar 27th. Please hand in paper copies
(preferably typeset, although hand-written copies will be accepted as well) for Questions 1 and 2. For
Question 3, you have to create scripts for the queries, and place them in your directory for the course.
Create a folder “HW3” under your main folder for the course, and put all queries in-order in a single file
named “Q3.sql”. Ensure that the file is not readable by others (comments in the SQL file to distinguish
between queries are expected, as this is a matter of good coding style).

Question 1 (20 points)

A university database contains information about professors (identified by social security number SSN)
and courses (identified by courseid). Professors also have a name, an address and a phone number.
Courses have a name and a number of credits. Professors teach courses. For each of the following
situations, draw an ER diagram that describes it (assuming no further constraints hold).

(a) Every professor must teach some course.
(b) Every professor teaches exactly one course (no more, no less).
(c) Every professor teaches exactly one course (no more, no less), and every course must be taught

by some professor.
(d) [630 students only] Modify the diagram from (a) such that a professor can have a set of addresses

(which are street-city-state triples) and a set of phones. Recall that in the E/R model there can be
only primitive data types (no sets).

(e) [630 students only] Modify the diagram from (d) such that professors can have a set of addresses,
and at each address there is a set of phones.

Question 2 (15 points)

Let a and b be integer-valued attributes that may be NULL in some tuples. For each of the following
conditions that may appear in a WHERE clause, describe exactly the set of (a,b) tuples that satisfy the
condition, including the case where a and/or b is NULL.

(a) a=10 OR b=20

(b) a=10 AND b=20
(c) a<10 OR a>=10
(d) [630 students only] a=b

Question 3 (15 points)

Consider a database schema with three relations:

Employee (eid:integer, ename:string, age:integer, salary:real)

Works (eid:integer, did:integer, pct_time:integer)

Department(did:integer, dname:string, budget:real, managerid:integer)

The keys are underlined in each relation. Relation Employee stores employee information such as

unique identifier eid, employee name ename, age and salary. Relation Department stores the
department unique identifier did, department name dname, the department budget and managerid
which is the eid of the employee who is managing the department. The managerid value must always
be found in the eid field of a record of the Employee relation. The Works relation tracks which
employee works in which department, and what percentage of the time s/he allocates to that
department. Note that, an employee can work in several departments.

Provide SQL statements for the following:

(a) Create a view ManagerSummary that lists for every department the department name,
manager ID and manager name, manager salary and the number of employees in that

department. The view will have five columns with headings: DeptName, MgrID, MgrName,
MgrSalary and EmpCount.

(b) Query the view above to retrieve the set of distinct salaries of managers who manage a
department called “Sales”.

(c) Query the view above to find the name of the manager who manages most employees. If the
same employee works in several departments, that employee is counted once in each of the
departments. The manager is included in the count the same as all other employees, i.e., based
on his or her records in the Works table.