Precedence graphs help to find a
Answer: A
Correct answer: Serializable schedule.
A precedence, or serialization, graph has a node per transaction and an edge for each conflicting pair. If the graph has no cycle the schedule is serializable; a cycle means it is not. Deadlock is detected with a different graph, the wait-for graph.
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A relation is in ______ if an attribute of a composite key is dependent on an attribute of another composite key.
Answer: B
Correct answer: 3NF
This is the transitive dependency that third normal form forbids: a non-key attribute determining another non-key attribute. Second normal form removes only partial dependencies on part of a composite key, so the relation can satisfy 2NF and still fail here.
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As per equivalence rules for query transformation, selection operation distributes over
Answer: D
Correct answer: All of the above.
Selection can be pushed through any of the three set operations, since deciding whether a tuple satisfies a condition does not depend on which relation it came from:
\[ \sigma_\theta(R \cup S) = \sigma_\theta(R) \cup \sigma_\theta(S) \]
and the same holds for intersection and difference. Doing the selection first is what makes such transformations worth applying.
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In 2NF
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.
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DROP is a statement in SQL.
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.
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For correct behaviour during recovery, undo and redo operation must be
Answer: C
Correct answer: idempotent
Recovery may be interrupted and restarted, so an undo or redo may be applied more than once to the same record. The operations are therefore written to be idempotent: applying them twice leaves the same result as applying them once.
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Key to represent relationship between tables is called
Answer: C
Correct answer: foreign key
A foreign key is a column whose values must appear as a primary key in another table, and that requirement is what represents the relationship between the two. A primary key identifies rows within one table only.
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The values of the attribute describes a particular
Answer: C
Correct answer: Entity instance
A particular set of attribute values describes one particular thing - one entity instance, or occurrence. The entity set is the collection of all such instances of the same type.
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The clause in SQL that specifies that the query result should be sorted in ascending or descending order based on the values of one or more columns is
Answer: B
Correct answer: Order by
ORDER BY sorts the result, taking ASC or DESC and one or more columns. GROUP BY collects rows into groups and HAVING filters those groups; neither of them sorts.
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______contains information that defines valid values that are stored in a column or data type.
Answer: B
Correct answer: Rule
A rule is bound to a column or a user-defined data type and specifies which values are acceptable there. A default supplies a value when none is given, and an index affects only how rows are found.
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