Database Design Multiple Choice According to class material, which of the follow

Question

Database Design Multiple Choice

According to class material, which of the following statement is true? (a) When we do an "equijoin" on two tables, the two columns used for matching attribute values between the two table do not need to have the same attribute name. (b) When we do an "equijoin" on two tables, the two columns of values compared to pick the qualifying records must have the same attribute name. (c) When we do a "theta" join on two tables, the two columns of values compared to pick the qualifying records must have the same attribute name. (d) When we do a "natural join" on two tables, the two columns of values compared to pick the qualifying records do not need to have the same attribute name. (e) None of (a) through (d) is the correct answer.

Explanation / Answer

Definations:
1. Theta join: Theta join combines tuples from different relations provided they satisfy the theta condition. So option c is not correct.

2. Equijoin: When Theta join uses only equality comparison operator, it is said to be equijoin. So we can say option a is correct and option b is not correct

3. Natural join: Natural join does not use any comparison operator. It does not concatenate the way a Cartesian product does. We can perform a Natural Join only if there is at least one common attribute that exists between two relations. In addition, the attributes must have the same name and domain. So oviously option d is incorrect.

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So the most apt solution is a as I have already described!

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