Suppose the following tables are part of a project management database of a company, where keys are underlined: E(ssn, name, salary) stores the information of employees, P(pid, title, budget) stores the information of projects, and M(ssn, pid, start, end) stores the information of management of projects by employees.

1.) Define an SQL view PNum (pid, num) that gives the number of employees that manages project pid.

2.) Write an SQL query to return the ssn of employees that manage each project in P.

3.) Write an SQL CREATE ASSERTION statement to force the constraint An employee needs to manage at least one project

4.) Write an SQL CREATE ASSERTION statement to enforce the constraint that an employee never manages two projects that overlap in time.

5.) Define an SQL view Budget(ssn, totalbudget) that summarizes the total budget of projects that an employee manages.