GATE CS 2013 Q.15 (CS Q.15): File Organization, B-Trees and B+ Trees Indexing

An index is clustered, if

it is on a set of fields that form a candidate key.

it is on a set of fields that include the primary key.

the data records of the file are organized in the same order as the data entries of the index.

the data records of the file are organized not in the same order as the data entries of the index.

Official answer and solution

Official answer: C
From: Official GATE 2013 answer key

Solution

Recall the fundamental relational database definition of a clustered index.

By standard database definition:

A clustered index is an index where the physical order of the rows in the data file corresponds directly to the logical (search-key) order of the index records.
Because physical storage can only have one physical sort order, a table can have at most one clustered index.
Non-clustered (secondary) indices maintain pointers to rows whose physical ordering does not match the index key order.

Therefore, an index is clustered if 'the data records of the file are organized in the same order as the data entries of the index' (Option C).

Final answer

Option (C)

Common trap

Confusing a clustered index with a primary index (which requires the key to be a candidate or primary key, whereas a clustered index can be on non-key attributes as well).

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2013 Computer Science and Information Technology (CS)
Question: 15 of 65, printed as CS Q.15
Section: Computer Science and Information Technology

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