Oracle PL/SQL Online Test

Consider the following code:

CREATE OR REPLACE FUNCTION count_users 
RETURN NUMBER 
IS 
  user_count NUMBER;
BEGIN
  SELECT COUNT(*) INTO user_count FROM users;
  RETURN user_count;
END;
/

Select the statements that are correct.

App usage data are kept in the following table:

TABLE sessions
  id INTEGER PRIMARY KEY,
  userId INTEGER NOT NULL,
  duration DECIMAL NOT NULL

Write a query that selects userId and average session duration for each user who has more than one session.

See the example case for more details.

The following data definition defines an organization's employee hierarchy.

An employee is a manager if any other employee has their managerId set to this employee's id. That means John is a manager if at least one other employee has their managerId set to John's id.

TABLE employees
  id INTEGER NOT NULL PRIMARY KEY
  managerId INTEGER
  name VARCHAR(30) NOT NULL
  FOREIGN KEY (managerId) REFERENCES employees(id)

Write a query that selects only the names of employees who are not managers.

See the example case for more details.

Consider the following table definition:

CREATE TABLE couples(
  id NUMBER PRIMARY KEY NOT NULL,
  first_name VARCHAR2(50) NOT NULL,
  last_name VARCHAR2(50) NOT NULL
);

Later the following code is executed:

DECLARE
  husband_id NUMBER;
BEGIN
  SELECT id INTO husband_id FROM couples WHERE first_name = 'John' AND last_name = 'Johnson';
  INSERT INTO couples(id, first_name, last_name) VALUES(husband_id + 1, 'Jane', 'Johnson');
END;

Select the exceptions that might be raised.

Consider the following database objects:

CREATE TABLE states (
  state_code VARCHAR2(2) PRIMARY KEY NOT NULL
);

CREATE OR REPLACE PROCEDURE insert_state(new_state_code IN VARCHAR2) IS
BEGIN
  INSERT INTO states(state_code) VALUES (new_state_code);
  EXCEPTION
    WHEN OTHERS THEN
      dbms_output.put_line('Unable to insert state.');  
      ROLLBACK;
END;
/

Immediately upon their creation, the following code is executed:

BEGIN
  insert_state('NY');
  COMMIT;
  insert_state('CA');
  insert_state('CA');
  COMMIT;
  EXCEPTION
    WHEN OTHERS THEN
      dbms_output.put_line('An error occurred.');
      ROLLBACK;
END;
/

Select the statements that are correct.

Given the following data definition, write a query that returns the number of students whose first name is John.

TABLE students
   id INTEGER PRIMARY KEY,
   firstName VARCHAR(30) NOT NULL,
   lastName VARCHAR(30) NOT NULL

A table containing the students enrolled in a yearly course has incorrect data in records with ids between 20 and 100 (inclusive).

TABLE enrollments
  id INTEGER NOT NULL PRIMARY KEY
  year INTEGER NOT NULL
  studentId INTEGER NOT NULL

Write a query that updates the field 'year' of every faulty record to 2015.

Information about pets is kept in two separate tables:

TABLE dogs
  id INTEGER NOT NULL PRIMARY KEY,
  name VARCHAR(50) NOT NULL

TABLE cats
  id INTEGER NOT NULL PRIMARY KEY,
  name VARCHAR(50) NOT NULL

Write a query that select all distinct pet names.

See the example case for more details.

A new social network site has the following data tables:

Select data that will be returned by the following SQL query:

SELECT users.name, COUNT(*) as count FROM users
LEFT JOIN friends
ON users.id = friends.user1 OR users.id = friends.user2
WHERE users.sex = 'f'
GROUP BY users.id, users.name;

Each item in a web shop belongs to a seller. To ensure service quality, each seller has a rating.

The data are kept in the following two tables:

TABLE sellers
  id INTEGER PRIMARY KEY,
  name VARCHAR(30) NOT NULL,
  rating INTEGER NOT NULL

TABLE items
  id INTEGER PRIMARY KEY,
  name VARCHAR(30) NOT NULL,
  sellerId INTEGER
  FOREIGN KEY (sellerId) REFERENCES sellers(id)

Write a query that selects the item name and the name of its seller for each item that belongs to a seller with a rating greater than 4. The query should return the name of the item as the first column and name of the seller as the second column.

See the example case for more details.

Consider the following code:

CREATE OR REPLACE PROCEDURE log_transaction(log_message VARCHAR2, log_level NUMBER) AS
  PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
  INSERT INTO logs(log_text, log_level) VALUES(log_message, log_level);

  IF log_level = 0 THEN
    ROLLBACK;
  ELSE
    COMMIT;
  END IF;
END;
/

Select the statements that are correct when calling this function within another transaction.

The following two tables are used to define users and their respective roles:

TABLE users
  id INTEGER NOT NULL PRIMARY KEY,
  userName VARCHAR(50) NOT NULL

TABLE roles
  id INTEGER NOT NULL PRIMARY KEY,
  role VARCHAR(20) NOT NULL

The usersRoles table should contain the mapping between each user and their roles. Each user can have many roles, and each role can have many users.

Modify the provided SQL create table statement so that:

• Only users from the users table can exist within usersRoles.
• Only roles from the roles table can exist within usersRoles.
• A user can only have a specific role once.

See the example case for more details.

An insurance company maintains records of sales made by its employees. Each employee is assigned to a state. States are grouped under regions. The following tables contain the data:

TABLE regions
  id INTEGER PRIMARY KEY
  name VARCHAR(50) NOT NULL

TABLE states
  id INTEGER PRIMARY KEY
  name VARCHAR(50) NOT NULL
  regionId INTEGER NOT NULL
  FOREIGN KEY (regionId) REFERENCES regions(id)

TABLE employees
  id INTEGER PRIMARY KEY
  name VARCHAR(50) NOT NULL
  stateId INTEGER NOT NULL
  FOREIGN KEY (stateId) REFERENCES states(id)

TABLE sales
  id INTEGER PRIMARY KEY
  amount INTEGER NOT NULL
  employeeId INTEGER NOT NULL
  FOREIGN KEY (employeeId) REFERENCES employees(id)  

Management requires a comparative region sales analysis report.

Write a query that returns:

• The region name.
• Average sales per employee for the region (Average sales = Total sales made for the region / Number of employees in the region).
• The difference between the average sales of the region with the highest average sales, and the average sales per employee for the region (average sales to be calculated as explained above).

Employees can have multiple sales. A region with no sales should be also returned. Use 0 for average sales per employee for such a region when calculating the 2nd and the 3rd column.

See the example case for more details.