MCQs on Data Definition Language (DDL) | Oracle Database Structure

Topic 1: Creating, Modifying, and Dropping Tables

1. Which DDL command is used to create a new table in a database?
   • A) ALTER TABLE
   • B) CREATE TABLE
   • C) DROP TABLE
   • D) MODIFY TABLE
2. What does the DROP TABLE command do in SQL?
   • A) Deletes all rows from a table without removing its structure
   • B) Modifies the structure of a table
   • C) Removes the table and its structure from the database
   • D) Adds a new column to the table
3. Which command would you use to remove a column from an existing table?
   • A) ALTER TABLE … DROP COLUMN
   • B) DELETE COLUMN
   • C) REMOVE COLUMN
   • D) DROP TABLE
4. What does the ALTER TABLE command allow you to do?
   • A) Change data in a table
   • B) Modify the structure of a table
   • C) Delete a table
   • D) Retrieve data from a table
5. Which command can change the data type of a column in an existing table?
   • A) MODIFY TABLE
   • B) ALTER TABLE
   • C) CHANGE TABLE
   • D) DROP TABLE
6. If you want to rename a table, which command would you use?
   • A) RENAME TABLE
   • B) MODIFY TABLE
   • C) ALTER TABLE … RENAME TO
   • D) CHANGE TABLE

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Topic 2: Creating and Managing Constraints (Primary Key, Foreign Key, Unique, etc.)

7. Which constraint ensures that all values in a column are unique?
   • A) CHECK
   • B) UNIQUE
   • C) PRIMARY KEY
   • D) FOREIGN KEY
8. What is the purpose of a primary key constraint in a table?
   • A) To allow NULL values in a column
   • B) To uniquely identify each record in a table
   • C) To reference another table
   • D) To store unique data
9. Which constraint is used to enforce a relationship between two tables?
   • A) UNIQUE
   • B) PRIMARY KEY
   • C) CHECK
   • D) FOREIGN KEY
10. When creating a primary key, what must be true about the column?

• A) It can contain NULL values
• B) It must contain unique values
• C) It can contain duplicate values
• D) It can reference another table

11. Which constraint prevents a NULL value from being entered in a specific column?

• A) PRIMARY KEY
• B) NOT NULL
• C) UNIQUE
• D) FOREIGN KEY

12. What does a CHECK constraint do in a table?

• A) Limits the range of values in a column
• B) Ensures uniqueness of values in a column
• C) Enforces relationships between tables
• D) Prevents NULL values

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Topic 3: Working with Indexes

13. What is an index in SQL?

• A) A command to add a new column
• B) A way to optimize data retrieval speed
• C) A way to delete records faster
• D) A command to create tables

14. Which command is used to create an index on a column?

• A) ALTER TABLE
• B) CREATE INDEX
• C) MODIFY INDEX
• D) ADD INDEX

15. What is a unique index?

• A) An index that only stores non-duplicate values
• B) An index that is automatically created by SQL
• C) An index created on a primary key column
• D) An index that can only be applied to string values

16. What is the main purpose of using indexes?

• A) To decrease data storage requirements
• B) To speed up retrieval of records
• C) To add more columns to tables
• D) To allow duplicate entries

17. How can you delete an existing index in SQL?

• A) DROP INDEX
• B) DELETE INDEX
• C) REMOVE INDEX
• D) ALTER INDEX

18. Which type of index would you use to ensure unique values in a column?

• A) Clustered Index
• B) Unique Index
• C) Foreign Key Index
• D) Sorted Index

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Topic 4: Creating and Managing Views

19. What is a view in SQL?

• A) A stored query that appears as a virtual table
• B) A physical copy of a table
• C) A way to store data on disk
• D) A command to modify tables

20. Which command is used to create a view in SQL?

• A) CREATE VIEW
• B) CREATE TABLE AS VIEW
• C) SELECT VIEW
• D) MODIFY VIEW

21. Can a view include data from multiple tables?

• A) No, it can only include data from one table
• B) Yes, it can include data from multiple tables
• C) Only if the tables have a primary key
• D) Only if the tables are in the same database

22. How do you remove a view from a database?

• A) DROP TABLE
• B) DROP VIEW
• C) DELETE VIEW
• D) REMOVE VIEW

23. Which command would you use to update an existing view?

• A) ALTER VIEW
• B) MODIFY VIEW
• C) CHANGE VIEW
• D) UPDATE VIEW

24. When is a view useful?

• A) For optimizing insert statements
• B) For creating backups
• C) For simplifying complex queries
• D) For permanently storing data

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Topic 5: Using Sequences and Synonyms

25. What is a sequence in SQL?

• A) A set of data points in a table
• B) An object that generates sequential numbers
• C) A command to update tables
• D) A way to delete records

26. Which command is used to create a sequence in SQL?

• A) CREATE TABLE
• B) CREATE SEQUENCE
• C) ALTER SEQUENCE
• D) NEW SEQUENCE

27. Which SQL function would you use to get the next value in a sequence?

• A) NEXT_VALUE
• B) NEXTVAL
• C) CURRENTVAL
• D) VALUE_INCREMENT

28. What is a synonym in SQL?

• A) A synonym is an alias for a table or other object
• B) A synonym is a primary key constraint
• C) A synonym is an index for a column
• D) A synonym is a unique constraint

29. Why might you create a synonym in a database?

• A) To increase data retrieval speed
• B) To simplify access to database objects
• C) To add constraints
• D) To create backups

30. How do you remove a sequence in SQL?

• A) DELETE SEQUENCE
• B) DROP SEQUENCE
• C) REMOVE SEQUENCE
• D) ALTER SEQUENCE

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Answers

Qno	Answer
1	B) CREATE TABLE
2	C) Removes the table and its structure from the database
3	A) ALTER TABLE … DROP COLUMN
4	B) Modify the structure of a table
5	B) ALTER TABLE
6	C) ALTER TABLE … RENAME TO
7	B) UNIQUE
8	B) To uniquely identify each record in a table
9	D) FOREIGN KEY
10	B) It must contain unique values
11	B) NOT NULL
12	A) Limits the range of values in a column
13	B) A way to optimize data retrieval speed
14	B) CREATE INDEX
15	A) An index that only stores non-duplicate values
16	B) To speed up retrieval of records
17	A) DROP INDEX
18	B) Unique Index
19	A) A stored query that appears as a virtual table
20	A) CREATE VIEW
21	B) Yes, it can include data from multiple tables
22	B) DROP VIEW
23	A) ALTER VIEW
24	C) For simplifying complex queries
25	B) An object that generates sequential numbers
26	B) CREATE SEQUENCE
27	B) NEXTVAL
28	A) A synonym is an alias for a table or other object
29	B) To simplify access to database objects
30	B) DROP SEQUENCE