MadeEasyTest #Query

Question

Answer 1

This is an example of Double Nested NOT EXISTS query. That is, it has a NOT EXISTS clause within a 

NOT EXISTS clause. Formally, it answers the question “does an employee exist with projectname Database and a project that is not in Works”? But it is easier to say that a nested NOT EXISTS answers the question 

“is x TRUE for all y?”

In our case, that is equivalent to "Find the employees whos age is more than 30 and works for every project  with project name database"

Answer 2

R1 = All project pid's which are under at least 1 employee.
R2 = (all  pid's whose pname is database which are not under any employee ) =[ (project name = database) and not exist R1].
R3= (employee which is working on every project whoose project name is database) and whose age>30 and not in R2.

WHY EVERY : becuase we had eliminated all project whoose name is database and not under any employee.