The ______ key of a relation is the attribute (column) or collection of attributes, which uniquely identify a given tuple.
Answer: A
Correct answer: Primary
The primary key is the attribute or set of attributes chosen to identify each tuple uniquely. Candidate keys are all those that could serve; the one selected becomes the primary key and the rest are alternates.
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The size of a data item is called its _______, which can be a field of some record or may be a larger unit such as a record.
Answer: B
Correct answer: Granularity
Granularity is the size of the item a lock or an operation applies to - a field, a record, a page, a whole table. Fine granularity allows more concurrency but costs more in locking overhead, which is the trade-off the term exists to describe.
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In E-R Diagram total participation is represented by
Answer: A
Correct answer: Double lines
Double lines joining an entity to a relationship indicate total participation - every entity in the set must take part. A single line indicates partial participation.
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In SQL the word natural can be used with
Answer: C
Correct answer: all of the above
Natural describes how the join columns are chosen - automatically, from the columns the two tables share - and that is independent of whether the join is inner, left, right or full. So it can be combined with any of them.
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_______ product was acquired by Informix, integrated into its RDBMS and introduced as the Informix Universal Server an ORDBMS.
Answer: B
Correct answer: Illustra
Illustra, the object-relational system built on the Postgres research work, was bought by Informix and became the Informix Universal Server.
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Union operator is a :
Answer: C
Correct answer: Binary Operator
Union takes two relations and produces one, so it is binary. Selection and projection are unary; there are no ternary operators in relational algebra.
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The ______ indexes are forced to store only record IDs in the data structure and require at least one additional I/O Operation to retrieve the actual record.
Answer: C
Correct answer: Un-clustered
In a clustered index the rows are held in index order, so reaching the index entry reaches the row. An un-clustered index stores only a pointer or record id, so a second access is needed to fetch the row itself.
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A _____ is a logical unit of database processing that includes one or more data access operations that can include insertion, deletion, modification or retrieval operations.
Answer: C
Correct answer: Transaction
A transaction is the unit of database processing: a group of operations that must all take effect or none, so that the database moves from one consistent state to another. That is what makes it the unit for recovery and concurrency control.
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What is a disjoint less constraint?
Answer: A
Correct answer: It requires that an entity belongs to no more than one lower level entity set
A disjointness constraint on a specialisation says the lower-level sets do not overlap, so an entity may be a member of at most one of them. If it may belong to several, the specialisation is overlapping instead.
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Which of the following statement on the view concept in SQL is invalid?
Answer: D
Correct answer: The definition of a view should not have GROUP BY clause in it
A view definition may perfectly well contain GROUP BY - that is one of the commonest uses of a view, to present a summary. What such a view cannot generally do is accept updates, which is the true statement the first option makes.
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