Database Management System Questions and Answers

Answer: A

Correct answer: no redo

Shadow paging keeps the old page table until the transaction commits, and commits by switching to the new one atomically. So an aborted transaction is undone simply by discarding the new pages, and a committed one is already complete on disk - there is nothing to redo.

Answer: A

Correct answer: superkey

If the closure of an attribute set determines every attribute of the relation, that set identifies each tuple uniquely, which is the definition of a superkey. It is a candidate key only if no proper subset of it also determines the whole relation.

Answer: C

Correct answer: DDL

DROP removes a table, view or index - a change to the structure of the database - so it belongs to the Data Definition Language, alongside CREATE and ALTER.

Answer: D

Correct answer: inner join

An inner join returns only the pairs of rows that match, discarding unmatched rows from both sides. The outer joins exist precisely to keep them: left keeps the unmatched rows of R, right those of S, and full both.

Answer: C

Correct answer: DISTINCT

SELECT DISTINCT removes duplicate rows from the result. UNIQUE is a constraint declared on a column when the table is defined; it prevents duplicates being stored rather than filtering them out of a query.

Answer: C

Correct answer: No partial FDs exist.

Second normal form requires that every non-key attribute depend on the whole of the primary key, so a dependency on only part of a composite key - a partial functional dependency - is what 2NF eliminates. Transitive dependencies are left to 3NF.

Answer: D

Correct answer: (ii) and (iii)

Logical data independence protects programs from changes to the logical structure: adding an entity or splitting a record leaves existing programs working, because they still see the fields they asked for. Changing access methods or the storage structure is a change at the physical level, and immunity to those is physical data independence.

Answer: C

Correct answer: Operationally, if X is deleted, so is Y.

X is the subordinate, so it depends on Y and not the other way round: deleting the dominant entity Y removes the subordinate X, but deleting X leaves Y untouched. The keyed statement reverses that dependence.

Answer: C

Correct answer: Procedural query Language

Relational algebra is procedural: an expression specifies a sequence of operations - select, then project, then join - and so says how the result is to be obtained. Relational calculus and SQL are declarative by contrast.

Answer: B

Correct answer: COUNT (*)

Every aggregate ignores nulls, because a null is not a value to be counted or summed. COUNT(*) is the exception: it counts rows rather than values, so a row consisting entirely of nulls is still counted.