Question: If we want to include attributes from two different relations, which of the following operations is needed?
Answer:
Consider a Query to find the names of all bank customers who have either an account or a loan or both. Note that the customer relation does not contain the information, since a customer does not need to have either an account or a loan at bank. To answer this query we the information in the depositor relation and in the borrower relation.
So the expression needed is
Π customer-name (borrower) U Π customer-name (depositor)
MCQ: If we want to include attributes from two different relations, which of the following operations is needed?
Explanation:
Consider a Query to find the names of all bank customers who have either an account or a loan or both. Note that the customer relation does not contain the information, since a customer does not need to have either an account or a loan at bank. To answer this query we the information in the depositor relation and in the borrower relation.
So the expression needed is
Π customer-name (borrower) U Π customer-name (depositor)
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Related Questions
- 1. Which of the following operation allows us to find the tuples that are in one relation but are not in another relation?
- 2. Which of the following operation, denoted by cross (×), allows to combine the information from any two relation.
- 3. Suppose we wish to find all customers who have both a loan and an account. Which of the following operation allows us to produce this relation?
- 4. Which of the following operation that allows us to combine certain selections and a Cartesian product into one operation?
- 5. Natural join operation is denoted by symbol____
- 6. It is convenient at times to write a relational algebra expression by assigning parts of it to temporary relation variables. Which of the following operation will be used for that?
- 7. Which of the following symbol can be used for Assignment operation in the relational algebra expression?
- 8. Which of the following take a collection of values and return a single value as a result?
- 9. Which of the following operation behave just like join operations except on tuples that do not occur in the join results?
- 10. Which of the following Statements stands true for Left outer-join? <ol> <li>The left outer join takes all tuples in the left relation that did not match with any tuple in the right relation, pads the tuples with null values for all other attributes from the right relation, and add them to the result of the natural join.</li> <li>It pads tuples from the right relation that did not match any from the left relation with nulls and adds them to the result of the natural join.</li> <li>it pads tuples from the left relation that did not match any from the right relation,as well as tuples from the right relation that did not match any from the left relation,abd adding them to the result of join</li> <li>It takes all tuples in the right relation that did not match with any tuple in the right relation, pads the tuples with null values for all other attributes from the right relation, and add them to the result of the natural join.</li> </ol>
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