Relation R has 4 tuples and 3 attributes, and S has 5 tuples and 2 attributes, with no attribute names in common. How large is the Cartesian product R x S?
Correct answer D. 20 tuples, 5 attributes
Subject / 421 questions
Programming MCQs
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Which of these relational algebra operations is not one of the basic operations, because it can be expressed using a Cartesian product followed by a selection and projection?
Correct answer A. Natural join
Relation R(A, B, C, D, E) has functional dependencies A -> B, B -> C and CD -> E. What is the attribute closure {A}+?
Correct answer B. {A, B, C}
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Relation R(A, B, C, D, E) has functional dependencies A -> B, B -> C and CD -> E. Which of these is a candidate key of R?
Correct answer C. AD
Enrol(student_id, course_id, student_name, grade) has key (student_id, course_id), with student_id -> student_name and (student_id, course_id) -> grade. Which normal form does it fail first?
Correct answer C. 2NF
Emp(emp_id, dept_id, dept_name) has key emp_id, with emp_id -> dept_id and dept_id -> dept_name. What is the highest normal form this relation satisfies?
Correct answer B. 2NF
R(A, B, C) has functional dependencies AB -> C and C -> B, so its candidate keys are AB and AC. Which statement is true?
Correct answer A. R is in 3NF but not in BCNF
A Student table stores several phone numbers in one column as a comma-separated string such as ‘0300-1111111, 0321-2222222’. Which normal form does this violate?
Correct answer B. First normal form
An unnormalised table records (student, course, course_fee). When the last student enrolled in a course withdraws and the row is deleted, the course fee is lost too. Which anomaly is this?
Correct answer A. Deletion anomaly
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R(A, B, C) has the single functional dependency B -> C. Which decomposition of R is lossless-join?
Correct answer B. R1(A, B) and R2(B, C)
Which statement about decomposing a relation is always true?
Correct answer A. A lossless, dependency-preserving decomposition into 3NF always exists
Which of the following SQL commands is a Data Definition Language (DDL) command?
Correct answer B. ALTER
You want to empty a large table of all its rows quickly while keeping the table structure for reuse, without row-by-row processing. Which command is designed for this?
Correct answer D. TRUNCATE TABLE t;
User ali was earlier given SELECT on table Emp. Which statement correctly withdraws that privilege?
Correct answer C. REVOKE SELECT ON Emp FROM ali;
What does adding WITH GRANT OPTION to GRANT SELECT ON Emp TO sara allow sara to do?
Correct answer B. Grant SELECT on Emp to other users
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Inside a transaction you run two UPDATE statements and then realise they were wrong. Which command undoes all changes made since the transaction began?
Correct answer D. ROLLBACK
Why does SELECT dept FROM Emp WHERE AVG(salary) > 5000 GROUP BY dept fail, while the same condition written in HAVING works?
Correct answer A. WHERE filters individual rows before groups and aggregates exist
Which LIKE pattern matches only strings that are exactly four characters long and end in ‘k’?
Correct answer C. '___k'
Which join returns every row from both tables, filling the columns of the other table with NULL wherever no match exists?
Correct answer A. FULL OUTER JOIN
What makes a subquery a correlated subquery?
Correct answer D. It refers to a column of the outer query, so it is evaluated for each outer row