In Oracle Database design, which option lists the main types of constraints that can be defined on table columns?

Introduction / Context:
This question explores the concept of constraints in Oracle Database. Constraints are rules enforced by the database to maintain data integrity. They ensure that the data stored in tables meets specific conditions, such as uniqueness or valid relationships between tables. Knowing the standard constraint types is a basic requirement for relational database design.

Given Data / Assumptions:

- The context is Oracle or similar relational databases with constraint support.
- Constraints are defined on tables and columns to enforce data integrity rules.
- Only one option lists valid constraint types rather than SQL statements or operators.

Concept / Approach:
The standard constraint types in Oracle are NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK. NOT NULL ensures that a column cannot store null values. UNIQUE enforces uniqueness of values in a column or group of columns. PRIMARY KEY combines NOT NULL and UNIQUE, providing a unique identifier for each row. FOREIGN KEY enforces referential integrity between parent and child tables. CHECK allows you to specify custom Boolean expressions that values must satisfy.

Step-by-Step Solution:
Step 1: Recall the list of constraint types from basic database design theory. Step 2: Review option A and confirm that it includes NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK, which are exactly the standard types. Step 3: Examine option B, which lists DDL commands CREATE, ALTER, DROP, and TRUNCATE, which are not constraints but operations on objects. Step 4: Look at option C, which lists DML commands SELECT, INSERT, UPDATE, DELETE, again not constraints. Step 5: Option D lists logical operators AND, OR, NOT, and BETWEEN, which are used in conditions but are not constraint types themselves.

Verification / Alternative check:
You can check USER_CONSTRAINTS in Oracle, which lists constraints for tables. The CONSTRAINT_TYPE column shows codes such as C for CHECK, P for PRIMARY KEY, U for UNIQUE, R for referential (foreign key), and N for NOT NULL. This system view confirms that option A aligns with the real constraint types supported by the database engine.

Why Other Options Are Wrong:
Option B is wrong because CREATE, ALTER, DROP, and TRUNCATE are Data Definition Language operations, not rules enforced on data. Option C lists Data Manipulation Language commands that operate on data but do not define integrity rules. Option D lists logical operators that may appear inside CHECK constraints but are not constraints by themselves.

Common Pitfalls:
A frequent mistake is to rely only on application code for validation instead of using database constraints. This can lead to inconsistent data if multiple applications access the database. Another pitfall is misusing FOREIGN KEY constraints without proper indexing or cascading options, which may cause performance or maintenance problems. Understanding each constraint type and its role helps design robust schemas.

Final Answer:
The main types of constraints are NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK, which are correctly grouped together in the given option.