What is DDL & DML ?

Question 1

What is the purpose of the **PRIMARY KEY** constraint in a **CREATE TABLE** statement?

A.

A) To uniquely identify each row in the table

Explanation: A **primary key** ensures each row has a unique identifier, preventing duplicates and null values.

B.

B) To allow duplicate values in a column

C.

C) To link columns between unrelated tables

D.

D) To store variable-length strings

Question 2

Why is a junction table like EmployeeProjects necessary?

A.

A) To store department locations

B.

B) To handle one-to-one relationships

C.

C) To manage many-to-many relationships

**Explanation:** It resolves many-to-many links between Employees and Projects using a **composite primary key**.

D.

D) To define primary keys only

Question 3

What happens if a **foreign key** references a non-existent **primary key** in the parent table?

A.

A) The row is automatically inserted

B.

B) The insertion fails due to referential integrity

**Explanation:** Foreign keys enforce referential integrity, preventing references to non-existent primary keys.

C.

C) Duplicates are allowed

D.

D) The primary key is created automatically

Question 4

What is the primary purpose of the **INSERT** statement in SQL?

A.

A) To retrieve data from a table

B.

B) To modify existing data in a table

C.

C) To add new rows to a table

**Explanation:** The INSERT statement is a DML command used specifically to populate tables with new data rows.

D.

D) To remove rows from a table

Question 5

Which INSERT statement is valid when omitting column names?

A.

A) Values in random order

B.

B) Values matching exact table column sequence

**Explanation:** Omitting column names requires values to follow the precise sequence defined in the table schema.

C.

C) Only numeric values allowed

D.

D) NULL values in any position

Question 6

What happens when inserting NULL into a column defined as NOT NULL?

A.

A) Insertion succeeds with default value

B.

B) MySQL automatically converts to zero

C.

C) Insertion fails with an error

**Explanation:** NOT NULL constraints require actual data; NULL insertion violates this and prevents the operation.

D.

A) Insertion succeeds with default value

📝 What is DDL & DML ?

Quiz Complete!