Which of the following statements about index is NOT true

Question

BlackTom AI · Accepted Answer

An index in a database is a data structure (commonly a B-tree or hash) that maps key values to a location reference so the DBMS can retrieve rows faster without scanning the entire table.

1) Relevant knowledge points and concepts
- Indexes store keys and references (pointers) to rows; they are typically implemented as B-trees or hashes and stored in a binary format not intended for direct human reading.
- For very small tables, a full table scan can be faster than using an index because of I/O and traversal overhead.
- Indexes usually store only keys and pointers (or compressed keys), so their storage footprint is typically smaller than the full table rows.
- Different RDBMS implement row location differently: some use ROWID-like identifiers, others use page number + slot or clustered storage; there is no single universal “record number” used by all RDBMS.

2) Step-by-step reasoning
- Evaluate option 1: “Indexes may be stored in a non-human readable format.” This is true: index structures are binary and implementation-specific.
- Evaluate option 2: “For small tables indexes do not speed up finding data.” This is generally true: cost of index traversal can exceed a sequential scan for small row counts.
- Evaluate option 4: “Indexes are usually smaller than the tables they index.” True in typical cases because indexes store keys and pointers only, not full row data.
- Evaluate option 3: “RDBMS uses a record number to locate a record in the table on the disk.” This is an overgeneralization and therefore NOT true as stated. While some systems expose ROWID or use fixed record numbers, many RDBMS use page/slot addresses, clustered index pointers, or complex storage engines — there is no universal “record number” mechanism across all RDBMS.

3) Why the correct answer is correct
Option 3 is incorrect because it asserts a universal mechanism that does not hold for all RDBMS implementations; index references are implementation-specific and not necessarily a simple record number.

4) Why the other options are incorrect as answers
Options 1, 2 and 4 are accurate general statements about indexes and therefore are not the NOT-true choice.

Conclusion: The statement “RDBMS uses a record number to locate a record in the table on the disk” is NOT true (option 3), matching the provided answer.

Which of the following statements about index is NOT true单项选择题

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Which of the following statements is true? Select one answer.

Which of the following statements is true? Select one answer.

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