Database Management Systems Laboratory Activity #05d

During this activity, you should:

learn more about the differences between Oracle and MySQL

learn how top-N queries are implemented in Oracle

learn how subqueries and set operators are implemented in Oracle

develop further existing skills in using the SQL SELECT statement to extract data from a database

I. Set Operators in Oracle Set operators (union, intersection, set difference) in MySQL are implemented via the UNION [ALL], IN (with subqueries) and NOT IN (with subqueries) operators. Although Oracle provides the same functionality and complies with the same guidelines on set operators (see Activity 4c), it provides direct implementations of intersection and set difference via the INTERSECT and MINUS operators.

II. Views

A view is a logical (or virtual) table based on one or more tables or views. A view contains no data itself. The

SELECT statement associated with the view is executed when the view is opened. Queries can use not only physical tables but also views as data sources (tables found in the FROM clause).

Views in MySQL:

Q6. Create a view that determines the top 5 busiest actors (based on the number of films that they have appeared in). Indicate the name of the view and SQL statement used in the view.

Heading of the view: actor_id, last_name, first_name, numfilms Required: first and last rows

Q7. Using the view created above and other relevant tables in the sakila schema, provide the SQL statement that displays the films of these 5 actors.

Heading: actor_id, last_name, first_name, title

Result: 199 rows Required: 5th row

Q1. Consider the UNION query below. How many rows does it return and what information does it

provide? SELECT DISTINCT m.last_name, m.first_name FROM employees e JOIN employees m ON e.manager_id = m.employee_id UNION SELECT DISTINCT last_name, first_name FROM departments d JOIN employees m ON d.manager_id = m.employee_id;

Q2. Provide the SQL statements that implements the corresponding intersection operation for the

above query. Use the INTERSECT keyword. Indicate also the number of rows that are returned by the query.

Q3. Provide the SQL statements that implements the corresponding set difference operations for the above query. Use the MINUS keyword. There should be two queries, since the set difference operation is not commutative. Indicate also the number of rows that are returned by each query.

Q4. Provide the SQL statement that determines the salaries common to departments 30 and 50. Heading: Salary

Result: 5 rows

Q5. Provide the SQL statement that determines the departments that do not have employees who

have salaries below 5000.

Heading: Department_Name Result: 7 rows

Views in Oracle

Q12. Create a view that provides information on all employees and their corresponding managers. All

employees should be included in the results generated from the view.

Heading of the view: EmpLast, EmpFirst, Salary, MgrLast, MgrFirst

Result: 107 rows

Required: Name of the view and the SQL statement used in the view

Q13. Using the view in Q12, provide the SQL statement that determines the employee under King who

gets the lowest salary.

Heading: EmpLast, EmpFirst, Salary

Required: resulting row

Q8. Create a view displays all countries along with the languages spoken in these countries and the

corresponding speaking population for each spoken language. The number of speakers should be

expressed (rounded up) as whole numbers. Heading of the view: Country, Language, NumSpeakers

Result: 984 rows Required: Name of the view and the SQL statement used in the view

Q9. Using the view above, provide the SQL statement that displays the total number of speakers for a

given language. The list should be sorted by the total number of speakers (in descending order). Heading: Language Total Number of Speakers

Result: 457 Required: In what row is English found and what is its total speaking population?

Q10. Using the view in Q8 as the data source, create another view that determines, for each country,

its largest speaking population for a spoken language. Include only aggregate values that are greater than 0 (use the HAVING clause).

Heading of the view: Country, NumSpeakers

Result: 213 rows Required: Name of the view and the SQL statement used in the view

Q11. Using the two views created in Q8 and Q10, provide the SQL statement (use the appropriate join

operation) that will display the top spoken languages for each country, along with its speaking

population.

Heading of the view: Country, Language, NumSpeakers Result: 213 rows; 1st row - Afghanistan, Pashto, 11905280

Required: 10th row