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# Database MCQ - ER-model & Relational Model

46:

An instance of relational schema R (A, B, C) has distinct values of A including NULL values. Which one of the following is true?

 A. A is a candidate key B. A is not a candidate key C. A is a primary Key D. Both (A) and (C) Answer Report Discuss Option: B Explanation : Click on Discuss to view users comments. Write your comments here:
47:

Consider the join of a relation R with relation S. If R has m tuples and S has n tuples, then the maximum size of join is:

 A. mn B. m+n C. (m+n)/2 D. 2(m+n) Answer Report Discuss Option: A Explanation : Click on Discuss to view users comments. Write your comments here:
48:

The natural join is equal to :

 A. Cartesian Product B. Combination of Union and Cartesian product C. Combination of selection and Cartesian product D. Combination of projection and Cartesian product Answer Report Discuss Option: C Explanation : Click on Discuss to view users comments. Pushpraj Singh said: (5:46pm on Tuesday 12th March 2013) The right answer is C not DRef: Korth Book Write your comments here:
49:

Which one of the following is not true for a view:

 A. View is derived from other tables. B. View is a virtual table. C. A view definition is permanently stored as part of the database. D. View never contains derived columns. Answer Report Discuss Option: C Explanation : Click on Discuss to view users comments. Geetu said: (1:34am on Saturday 13th April 2013) I dont this is a correct answer...as the database stores the view definition only. is this wrong that view definition is stored in database? Javid said: (11:43am on Sunday 4th March 2018) Correct answer is D Write your comments here:
50:

A primary key if combined with a foreign key creates

 A. Parent-Child relationship between the tables that connect them. B. Many to many relationship between the tables that connect them. C. Network model between the tables that connect them. D. None of the above. Answer Report Discuss Option: A Explanation : Click on Discuss to view users comments. Write your comments here:

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