You are the DBA for the VeryFine Toy Company and create a relation called Employees with ?elds ename, dept, and salary. For authorization reasons, you also de?ne views EmployeeNames (with ename as the only attribute) and DeptInfo with ?elds dept and avgsalary. The latter lists the average salary for each department.
1. Show the view de?nition statements for EmployeeNames and DeptInfo.
2. What privileges should be granted to a user who needs to know only average department salaries for the Toy and CS departments?
3. You want to authorize your secretary to ?re people (you will probably tell him whom to ?re, but you want to be able to delegate this task), to check on who is an employee, and to check on average department salaries. What privileges should you grant?
4. Continuing with the preceding scenario, you do not want your secretary to be able to look at the salaries of individuals. Does your answer to the previous question ensure this? Be speci?c: Can your secretary possibly ?nd out salaries of some individuals (depending on the actual set of tuples), or can your secretary always ?nd out the salary of any individual he wants to?
5. You want to give your secretary the authority to allow other people to read the EmployeeNames view. Show the appropriate command.
6. Your secretary de?nes two new views using the EmployeeNames view. The ?rst is called AtoRNames and simply selects names that begin with a letter in the range A to R. The second is called HowManyNames and counts the number of names. You are so pleased with this achievement that you decide to give your secretary the right to insert tuples into the EmployeeNames view. Show the appropriate command and describe what privileges your secretary has after this command is executed.
7. Your secretary allows Todd to read the EmployeeNames relation and later quits. You then revoke the secretary’s privileges. What happens to Todd’s privileges?
8. Give an example of a view update on the preceding schema that cannot be imple-mented through updates to Employees.
9. You decide to go on an extended vacation, and to make sure that emergencies can be handled, you want to authorize your boss Joe to read and modify the Employees relation and the EmployeeNames relation (and Joe must be able to delegate authority, of course, since he is too far up the management hierarchy to actually do any work). Show the appropriate SQL statements. Can Joe read the DeptInfo view?
10. After returning from your (wonderful) vacation, you see a note from Joe, indicating that he authorized his secretary Mike to read the Employees relation. You want to revoke Mike’s SELECT privilege on Employees, but you do not want to revoke the rights you gave to Joe, even temporarily. Can you do this in SQL?
11. Later you realize that Joe has been quite busy. He has de?ned a view called All-Names using the view EmployeeNames, de?ned another relation called Sta?Names that he has access to (but you cannot access), and given his secretary Mike the right to read from the AllNames view. Mike has passed this right on to his friend Susan. You decide that, even at the cost of annoying Joe by revoking some of his privileges, you simply have to take away Mike and Susan’s rights to see your data. What REVOKE statement would you execute? What rights does Joe have on Employees after this statement is executed? What views are dropped as a consequence?