Question

The schema of a table is EMPLOYEE(emp_code, emp_name, designation, salary).

Write down the relational expressions for the following: 

1. To get the name and designation of all employees. 

2. To get the details of employees whose salary is above 25000. 

3. To get the names of employees who designation is Manager. 

4. To get the details of Managers with salary less than 25000.

Answer 1

1. π_{name, designation} (EMPLOYEE)

2. σ_salary>25000 (EMLOYEE)

3. π_name(σ_{designation=”Manager"} (EMPLOYEE))

4. σ_{designation = “Manager” and salary < 25000} (EMLOYEE).