Question

Consider the following relational database schema:

            employee(employee-name, employee-id, street, e-city)

            works(employee-id, company-id, salary)

            company(company-name, company-id, c-city)

            manages(employee-id, manager-id)

Specify the following queries on this database schema using the relational operators we discussed in class. Write your answers on a separate sheet of paper in the order that they are specified below.

1. Retrieve the name and address of employees who work for First Bank Corporation.

2. Retrieve the name, street address, and city of residence of all employees who work for Thrifty Industries and earn more than $10,000 per year.

3. Retrieve the name of all employees who live in the same city as the company for which they work.

4. Retrieve the name of all employees who live on the same street and in the same city as do their managers.

5. Retrieve the name of all employees who do not work for First Bank Corporation.

6. Retrieve the name of all employees who earn more than every employee of Small Bank Corporation.

7. (Assume that companies may be located in several cities) Retrieve all companies located in every city in which Thrifty Industries is located.

8. For each company, find the average salary of employees working for that company.

9. For each city, find the number of employees who work for at least one company in that city.

Answer 1

1. Retrieve the name and address of emplofyees who work for First Bank Corporation
   SELECT employee_name , street, e-city FROM employee WHERE comapany-name IN (SELECT company-name FROM company WHERE company-name ="First Bank Corporation")
2. Retrieve the name, street address, and city of residence of all employees who work for Thrifty Industries and earn more than $10,000 per year
   SELECT E.employee-name, street,city FROM employee as E, works as W where E.employee-name = W.employee-name and W.company-name = 'Thrifty Industries' AND salary > 10000
3. Retrieve the name of all employees who live in the same city as the company for which they work.
   SELECT E.employee-name from employee as E, works as W , Company as C where E.employee-name = W.employee-name and E.city = C.city and W.company-name = C.company-name
4. Retrieve the name of all employees who live on the same street and in the same city as do their managers.
   SELECT E1.employee-name From employee as E1, Employee as E2, Manages as M WHERE E1.employee-id = M.employee-id and E2.employee-id = M.manager-id AND E1.street = E2.street AND E1.city = E2.city
5. Retrieve the name of all employees who do not work for First Bank Corporation.
   SELECT employee-name FROM employee WHERE company-name IN (SELECT company-name FROM Works WHERE company-name != 'First Bank Corporation'
6. Retrieve the name of all employees who earn more than every employee of Small Bank Corporation.
   SELECT employee-name FROM employee WHERE salary > ( SELECT salary FROM works WHERE company-name = 'Small Bank Corporation')
7. Retrieve all companies located in every city in which Thrifty Industries is located.
   SELECT C.company-name FROM company C WHERE ( SELECT R.city FROM company R WHERE R.company-name = T.company-name) CONTAINS (SELECT S.city FROM company S WHERE S.company-name = 'Thrifty Industries')
8. For each company, find the average salary of employees working for that company.
   SELECT company-name FROM company GROUP BY company-name HAVING  AVG(salary) FROM works