Oracle Indexes — Identify the Statement That Is NOT True Which of the following statements about Oracle indexes is NOT correct? Select the single best answer.

Introduction:
Indexes are critical performance structures in Oracle, allowing the database to locate rows efficiently. However, not every popular statement about indexes is accurate. This question asks you to spot the incorrect statement regarding how indexes are created and used.

Given Data / Assumptions:

• Oracle supports B-tree and bitmap indexes, among others.
• Unique constraints are typically enforced using underlying unique indexes.
• Administrators and developers must know the proper DDL commands for index management.

Concept / Approach:
In Oracle, the direct DDL to create an index is CREATE INDEX (or CREATE BITMAP INDEX, etc.). While ALTER TABLE ADD CONSTRAINT UNIQUE may implicitly create a unique index, indexes themselves are not created by ALTER TABLE as a standalone index-creation command. Therefore, the statement “Indexes are created with the ALTER TABLE command” is not correct. The other statements reflect common best practices or capabilities: enforcing uniqueness, improving retrieval speed, indexing columns used in equality predicates, and the use of bitmap indexes on low-cardinality columns in analytic systems.

Step-by-Step Solution:
1) Recall the correct DDL for indexes: CREATE INDEX ...2) Note that ALTER TABLE is for table alterations and constraints; it may indirectly create an index via a UNIQUE/PRIMARY KEY constraint.3) Validate that performance and uniqueness statements are accurate.4) Select the incorrect statement: “Indexes are created with the ALTER TABLE command.”

Verification / Alternative check:
Oracle SQL Language Reference shows CREATE INDEX syntax; ALTER TABLE is not the canonical method for creating indexes except indirectly through constraints.

Why Other Options Are Wrong:

• A, B, C, E: Accurately reflect index roles and appropriate use cases.

Common Pitfalls:
Assuming a constraint and an index are interchangeable. Constraints enforce rules; indexes are physical structures that may support constraints.

Final Answer:
Indexes are created with the ALTER TABLE command.