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);
Answer:
Quality Of Service
Explanation:
Technology that manages data traffic to reduce packet loss, latency and jitter on the network. QoS controls and manages network resources by setting priorities for specific types of data on the network.
Answer:
What is the question here? lol
Explanation:
Answer:
Array: (a) All the messages a user has sent.
Variable: (b) The highest score a use has reached on the app. (c) A username and password to unlock the app.
Explanation:
An array generally has more than one value whereas a variable can only contain a single value at any particular point in time. In addition, a variable has a limit whereas an array does not have any maximum limit. Therefore, it can be concluded that option (a) will be stored as an array while options (b) and (c) will be stored as variables.
Answer: Isolation, Depression, Humiliation.
I hope this helps you out! ☺
