EPPS 6354 Assignment 4

https://www.db-book.com/university-lab-dir/sqljs.html

Question 1:

Weak entity sets is one where the relation with another entity set is required to uniquely identify an entr. This makes the set dependent on the identifying entity set, with primary key of the identifying entity bing needed to uniquely find entries. Any entity without this is a strong entity set.

An example of this week entity would be if I had a table with customers, containing a customer_id, payment_info, favorite_item and a separate table for orders that uses customer_id as an identifier, along with item_ordered, and price for example.

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Question 2:

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Question 3: Remaining Queries

3a)

In this situation, adding a natural join with section would not change the result as the attributes from takes and section match (course_id, sec_id, semester, year) so items would not be excluded. Additionally, all sections in takes are also found in sections, so there are no missing values that would be excluded.

3b)

3c)

select distinct employee.ID
from employee left outer natural join manages
where manager_id is null