In Oracle Database, what is an index and why is it used?

Introduction / Context:
Indexes are one of the most important performance features in relational databases such as Oracle. They support efficient data retrieval by providing quick lookup paths for rows based on one or more column values. Understanding what an index is and why it exists helps database designers and administrators tune queries and design schemas effectively.

Given Data / Assumptions:

• We are working with Oracle Database, but the concept also applies to other RDBMS products.
• The question asks for the definition and purpose of an index.
• Options mention schemas, views, backup files, and triggers.
• We assume basic knowledge of tables, rows, and columns.
• Indexes are associated with tables or clusters.

Concept / Approach:
An index is a separate data structure that stores key values and pointers to the corresponding rows in a table or cluster. The database uses this structure to find rows quickly without scanning the entire table. Indexes can be created on one or more columns and can be unique or non unique. They may be implemented using balanced tree structures or other algorithms, but the key idea is that they improve the performance of queries that filter or join on indexed columns.

Step-by-Step Solution:
Step 1: Recall that an index is not the table itself but a structure built on top of one or more table columns. Step 2: Recognise that the main purpose of an index is to speed up data retrieval for queries that search, filter, or join on the indexed columns. Step 3: Understand that indexes are associated with tables or clusters, and the database automatically maintains them when data changes. Step 4: Compare this understanding with the answer choices and identify the one that highlights improved speed of data retrieval based on key values. Step 5: Confirm that this option is consistent with Oracle documentation and general database theory.

Verification / Alternative check:
If you create an index on a frequently searched column and then examine query execution plans, you will see that the optimizer may choose index range scans instead of full table scans. This behaviour directly demonstrates that indexes provide faster access paths for queries. Oracle documentation formally defines indexes as schema objects that can speed up the retrieval of rows.

Why Other Options Are Wrong:
Option A describes a schema for user accounts and passwords, which relates more to security than to indexing. Option C mentions a view that shows recent rows, which is unrelated to the index concept. Option D refers to a backup file, not an index structure. Option E confuses indexes with triggers; triggers are procedural code blocks that respond to events, whereas indexes are data structures that support query performance.

Common Pitfalls:
Some learners mistakenly think that indexes always improve performance and should be created on every column, which is not true; indexes come with storage and maintenance overhead. Another pitfall is confusing primary keys and indexes; while primary keys are often supported by unique indexes, the concepts are not identical. It is also easy to assume that indexes rearrange the physical order of rows, when in many cases they simply store logical pointers to data pages.

Final Answer:
In Oracle Database, an index is a logical or physical structure associated with a table or cluster that improves the speed of data retrieval based on key values..