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:
It goes like:
public class Program
{
public static void main(String[] args)
{
int j=18;
int sum=0;
for (int i =1; i<7; i++)
{
sum=sum+(i*(j-2));
j=j-2;
}
System.out.println(sum);
}
}
Explanation:
<u>Variables used: </u>
j : controls the first number in product and decreases by 2 each time the loop runs.
sum: saves the values of addition as the loop runs.
Answer:
A peer-to-peer network is one in which two or more PCs share files and access to devices such as printers without requiring a separate server computer or server software. ... A P2P network can be an ad hoc connection—a couple of computers connected via a Universal Serial Bus to transfer files.
U can see the printscr botton at the top right of ur keyboard and then u can type paint and the control v.
Answer:
Differ in the quality of their transmission.
Explanation:
For example, when using the public phone box, wired transmission is done not wireless as in cell phones. Public phone box use electronic signals transmitted through a cable network to send voice data which are not very effective for long distance communication.
However, cell phones wirelessly send electromagnetic wave signal to a cell tower close to the caller and then the information is then transmitted to cell tower close to the receiver within a split of a second. This method of communication has much advantages.
