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:
Customer Table
- Customer name
- Customer id
Product Table
- Product id/number (primary key, auto increment)
- Product name
- Product sale price
Transactions Table
- Transaction Id
- Customer Id
- Product id
- Quantity
- Price
- Date
Explanation:
Natalie wants to fetch following information from database
- Look up customer name and sale price
- Sort items in db by product number
To lookup customer name and sale price perform a join on Transactions table and Customer table.Assuming database is build in mysql the query to fetch required results would be
select transction.productId,transaction.customerid,customer.customername from transactions join customer ON
customer.customerid=transcation.customerid
where productid="user provided product id of returned product"
For sorting products by number set produc number in product table a auto increment primary key
Answer:
When you use a WYSIWYG editor you typically specify the content and layout while the editor generates the HTML code
Explanation:
Required
Complete the blanks
In WYSIWYG, the user of the application provides contents to the WYSIWYG software and also designs the appearance; The appearance is referred to as the layout.
Throughout the design, the user will not use HTML codes; it is the duty of the WYSIWYG editor to generate HTML code based on the input designs by the user.
Runs out of memory
has uninitialized variables
uses undefined behaviour
Answer:
a) 0.843 years
b) 1.785 years
Explanation:
See attached pictures for detailed explanation.
