In Oracle Database and standard SQL, which subset of SQL commands is specifically used to define and modify database structures such as tables, indexes, and schemas?

Introduction / Context:
Structured Query Language, or SQL, is often divided into logical subsets such as Data Definition Language and Data Manipulation Language. Interviewers like to check whether candidates can clearly distinguish between commands that define the structure of a database and commands that manipulate the data stored inside those structures. This question asks which subset is responsible for defining and changing database objects such as tables and indexes in an Oracle Database or any other relational database management system.

Given Data / Assumptions:

• We are working with a relational database such as Oracle Database.
• We are interested in SQL commands that define or modify structures like tables, indexes, and views.
• We assume the standard classification of SQL subsets into Data Definition Language and Data Manipulation Language.

Concept / Approach:
Data Definition Language, usually shortened to DDL, includes commands such as CREATE, ALTER, and DROP. These commands define new tables, modify existing objects, and remove objects from the database. Data Manipulation Language, or DML, includes commands such as SELECT, INSERT, UPDATE, and DELETE, which operate on the rows of data stored inside tables. Since the question is clearly about structures, we must focus on the subset that deals with definitions and changes at the schema level, which is DDL.

Step-by-Step Solution:
Step 1: Recall that SQL is grouped into different subsets such as DDL, DML, DCL, and sometimes TCL. Step 2: Identify common DDL commands, for example CREATE TABLE, ALTER TABLE, DROP TABLE, CREATE INDEX, and DROP INDEX. Step 3: Identify common DML commands, for example INSERT INTO, UPDATE, DELETE FROM, and SELECT. Step 4: Note that DML commands operate on row data, whereas DDL commands operate on database object structures. Step 5: Since the question specifically mentions manipulating database structures including tables, the correct subset must be Data Definition Language.

Verification / Alternative check:
As an additional check, ask yourself whether you need to commit a DDL command in the same way as a DML command. In many systems, DDL commands cause implicit commits because they change the structure of the database and must be persisted. This is another sign that DDL and DML serve different purposes, and only DDL is concerned with defining database structures.

Why Other Options Are Wrong:
Option A: Data Manipulation Language only manipulates data inside tables and does not define or change table structures. Option C: Suggests that both subsets are used for structures, but DML does not create or modify tables or indexes. Option D: Is incorrect because Data Definition Language is a very well established subset of SQL used for this purpose.

Common Pitfalls:
A frequent confusion is to think that any SQL statement that changes something in the database must be DML. Another mistake is to forget that SELECT, although extremely common, is also part of DML and not DDL. Remembering concrete examples of DDL commands like CREATE TABLE and ALTER TABLE will help you quickly recall that DDL is the subset that defines and modifies database structures.

Final Answer:
The correct subset of SQL commands used to manipulate database structures is Data Definition Language (DDL).