Advantages of Internet:
1. Easy and fast access to information2. Up to date news information3. Communications made over internet connecting people around the world4. Convenience in doing like research where you can now do it at home instead of visiting libraries.
Disadvantages of Internet:
1. Possible theft of personal information2. Internet addiction which leads to social isolation3. Inappropriate Contents
For the view of Exercise 4.18, explain why the database system would not allow a tuple to be inserted into the database through this view.
For reference
For the database of Figure 4.12, write a query to find the ID of each employee with no manager. Note that an employee may simply have no manager listed or may have a null manager. Write your query using an outer join and then write it again using no outer join at all.
OUTER JOIN
select e.ID from employee e left outer join manages m on e.ID = m.ID
where m.manager_id is null;
NO OUTER
select e.ID from employee e where e.ID not in (select m.ID from manages m) or e.ID in (select m.ID from manages m where m.manager_id is null);
