Informatics for Economics II - Exercise 1 Prof. Dr. Michael Böhlen

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1 1 Informatics for Economics II - Exercise 1 Prof. Dr. Michael Böhlen Date: 7 October 2010 Submission date: 14 October 2010 (optional) A. Introduction The aim of this exercise is to get you familiar with Relational Algebra, as well as go through some basic SQL queries, that will help deepen your understanding. You can submit the answers on paper, but it is recommended to try your solutions (for the SQL part) on the database server you installed in Exercise 0. The database structure and data used throughout the SQL exercises can be created using the SQL Zoo script file, that is downloadable using the following link: At the end of this exercise sheet, you can find a table structure of the database filled with data. B. Exercises Exercise 1 Why is it important not to store all employee data in a single table in the database (opposed to having several tables with relations between them)? What are the implications of doing so? Construct a table that illustrates problems that may arise from having such a table that stores all employee details.

2 2 Exercise 2 The following two relations contain movie data offered by the students DVD stores. For each relation, suggest a candidate key and identify, if any, a foreign key attribute. X Y Z com Comedy 3.5 hor Horror 3 act Action 5 dra Drama 4 adv Adventure 3.5 A B C 1 Gone in 60 seconds act 2 Scream hor 3 Titanic dra 4 Die Hard act 5 American Pie com 6 The Dark Knight act 7 Indiana Jones adv 8 The Ring hor Exercise 3 For each of the following queries, describe the query and construct the resulting relation. (Use the Zoo schema mentioned in Section.A of this assignment as a reference for the table structure and instance) 1. σ Income>5000 Sex= w (Employee) 2. Π AHV (Employee AHV =EmpAHV ρ (EmpAHV,Cage Id) (Employee Cage)) 3. σ ManagerId=AHV (Department Employee) 4. σ Dep=1 Sex= w (Employee) Exercise 4 For this exercise, use the following table structure: Client(AHV, ClientName, Amount) Movie(MovieId, MovieName, Rating) Rental(MovieId, AHV, Date) Write the relational query that corresponds to the following description

3 1. Movies that were never rented 2. All movies that Chris ever rented 3. Total amount spent by clients who ever rented the movie named Lord of the Rings Write the description of the following relational queries 1. Π AHV (σ MovieId=7 (Rental)) Π AHV (σ MovieId=12 (Rental)) 2. Π ClientName (σ MovieId=1 (Rental) σ Amount>100 (Client)) 3 Exercise 5 Write down the queries that would produce the data for the following inquiries. Also provide the results obtained from your query. 1. The last name of all employees who have a salary of The first and last name of the head of the Customer service department 3. The first and last name of all female employees who earn at least Indicate the AHV insurance number and the department name of all employees who are not assigned to a cage 5. Indicate the first name and last name of the youngest employee 6. Reduce the salary of all employees who work in the Management department by 5% 7. Indicate the salary, first name, and last name of all employees assigned to all cages 8. The name of all animals, and the corresponding cage name where they stay in 9. The first and last name, department of all employees who are assigned to a cage that has some ongoing construction work 10. The number of employees assigned to each cage (include the cage name in the result)

4 4 Notes Expected responses are as follows: SQL code: SELECT * FROM Cage WHERE Cage Id = 1; Result: Cage Id Name Size Has Construction Work 1 Tropical For UPDATE statements, show all modified tuples, illustrating their old and new values. Exercise 6 Illustrate and explain the results of the following queries 1. SELECT a.firstname, a.lastname, t.description FROM Employee a, Employee Cage e, Animal t WHERE a.ahv = e.ahv AND e.cage Id = t.cage Id ORDER BY t.description; 2. SELECT e.ahv, SUM(k.Size) FROM Employee Cage e, Cage k WHERE e.cage Id = k.cage Id GROUP BY e.ahv; 3. SELECT AVG(a.Income), k.name FROM Employee a, Employee Cage e, Cage k WHERE e.cage Id = k.cage Id AND k.name= Tropical AND e.ahv = a.ahv GROUP BY k.name; 4. UPDATE Cage SET Size = Size * 1.2

5 5 WHERE Cage Id IN (SELECT Cage Id FROM Animal WHERE Age >= 4 ) ; Notes The expected answer is as follows: Write a short description of the query with all relevant details Specify the output data in table format (as described in Exercise 1 notes) Exercise 7 The following events cause changes in the database. Write the modification statements required to reflect the changes in the database. 1. A Marketing department is newly created. Emmy Noether got promoted to be the head of the new department. Her salary and supervisor remain unchanged. Don t forget to update the Employee table if necessary. 2. Penguins are set to leave the zoo due to whether conditions. 3. The giant tortoise Harriet was imported to the zoo on 24th of July Harriet is 176 years old and stays in the Tropical cage. 4. A new cage was built to accommodate special types of birds. The cage name is Birds, has a size of 1420 with no ongoing construction work. 5. A new employee in the Customer service department: Name: Regina Gehlen AHV number: 42 Date of birth: 17th of January 1964 Earns 4200 Supervisor: Mirella Freni Regina will be assigned to cages: Arctic and Safari and Birds

6 6 C. Database This section presents a copy of the database tables defined in the SQL script provided earlier. Please note the following points: underlined column names represent a primary key column dash-underlined column names illustrate a foreign key column Employee AHV Lastname Firstname Dep Date Of Birth Manager Income Sex 1 Heusli Kurt m 2 Tell Beate w 3 Becker Ruedi m 4 Frisch Boris m 5 Maradona Sonja w 6 Wagner Guiseppe m 7 Verdi Amando m 8 Freni Mirella w 9 Schlau Adam m 10 Braun Tanja w Cage Cage Id Name Size Has Construction Work 1 Tropical Arctic Continental Safari Wild west Aquarium 225 0

7 7 Department Department Id Name Manager Id 1 Health 6 2 Facility management 2 3 Feeding 4 4 Counter 5 5 Customer service 7 6 Management 8 Animal Animal Id Description Cage Id Arrival Date Age 1 Pinguin Elefant Buffel Fish Parrot Beer

8 8 Employee Cage AHV Cage Id