Database

DATABASE & TABLE CONCEPTS

MCQ 1: Purpose of CREATE DATABASE

What is the purpose of the following command?

CREATE DATABASE IF NOT EXISTS animaldb;

A. Creates a new database named animaldb only if it does not already exist
B. Deletes the existing database named animaldb

✅ Correct Answer: A

MCQ 2: Purpose of USE

What does the USE animaldb; command do?
A. Deletes the animaldb database
B. Selects animaldb as the active database for subsequent queries

✅ Correct Answer: B

MCQ 3: Purpose of DROP TABLE IF EXISTS

Why is this command used before creating a table?

DROP TABLE IF EXISTS animals;

A. To remove the table if it already exists and avoid errors
B. To permanently lock the table for editing

✅ Correct Answer: A

MCQ 4: AUTO_INCREMENT and PRIMARY KEY

What is the role of id INT AUTO_INCREMENT PRIMARY KEY?
A. Automatically generates a unique identifier for each record
B. Allows duplicate values in the id column

✅ Correct Answer: A

MCQ 5: NOT NULL Constraint

What does NOT NULL ensure in a column definition?
A. The column must always contain a value
B. The column can store duplicate values

✅ Correct Answer: A

MCQ 6: ENUM Data Type

What is the purpose of using ENUM('Male','Female')?
A. To restrict the column values to predefined options
B. To allow any text value in the column

✅ Correct Answer: A

MCQ 7: DEFAULT Keyword

What does DEFAULT 'Available' mean in a column definition?
A. The column will automatically get this value if none is provided
B. The column value cannot be changed later

✅ Correct Answer: A

MCQ 8: FOREIGN KEY with ON DELETE CASCADE

What happens when a record in animals is deleted?
A. Related records in animal_images are automatically deleted
B. The delete operation is blocked

✅ Correct Answer: A

MCQ 9: Purpose of INSERT INTO

What is the main function of the INSERT INTO statement?
A. To add new records into a table
B. To modify existing records

✅ Correct Answer: A

MCQ 10: Purpose of COMMIT

Why is the COMMIT; statement used?
A. To permanently save the changes made in the transaction
B. To undo all database changes

✅ Correct Answer: A

MCQ 11: SELECT * Statement

What does the following command do?

SELECT * FROM animals;

A. Displays all columns and rows from the animals table
B. Deletes all records from the animals table

✅ Correct Answer: A

MCQ 12: TIMESTAMP with DEFAULT CURRENT_TIMESTAMP

What is the purpose of this column definition?

created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP

A. Automatically stores the date and time when a record is created
B. Requires the user to manually enter date and time

✅ Correct Answer: A

MCQ 13: Purpose of IF NOT EXISTS

Why is IF NOT EXISTS used in CREATE statements?
A. To prevent errors if the database or table already exists
B. To force recreation every time

✅ Correct Answer: A

MCQ 14: Database vs Table

What is the correct relationship between a database and a table?
A. A database contains tables
B. A table contains databases

✅ Correct Answer: A

MCQ 15: Effect of DROP TABLE

What happens when DROP TABLE animals; is executed?
A. The table structure and all its data are permanently deleted
B. Only the data is deleted, table structure remains

✅ Correct Answer: A

DATA TYPES & STORAGE

MCQ 16: Purpose of VARCHAR

Why is VARCHAR used instead of CHAR for name columns?
A. It stores variable-length strings and saves space
B. It stores fixed-length strings only

✅ Correct Answer: A

MCQ 17: TEXT vs VARCHAR

Why is temperament defined as TEXT instead of VARCHAR(100)?
A. TEXT can store longer descriptions
B. TEXT stores only numeric values

✅ Correct Answer: A

MCQ 18: INT DEFAULT 0

What is the purpose of DEFAULT 0 in numeric columns?
A. Assigns 0 when no value is provided
B. Prevents the column from storing numbers

✅ Correct Answer: A

CONSTRAINTS & KEYS

MCQ 19: PRIMARY KEY Concept

Why is a PRIMARY KEY important?
A. It uniquely identifies each record in a table
B. It allows duplicate rows

✅ Correct Answer: A

MCQ 20: FOREIGN KEY Purpose

What is the main purpose of a FOREIGN KEY?
A. To enforce a relationship between two tables
B. To store duplicate values

✅ Correct Answer: A

MCQ 21: One-to-Many Relationship

What type of relationship exists between animals and animal_images?
A. One animal can have many images
B. One image can have many animals

✅ Correct Answer: A

MCQ 22: Referential Integrity

Which concept ensures that animal_id in animal_images must exist in animals?
A. Referential integrity
B. Data redundancy

✅ Correct Answer: A

MCQ 23: ON DELETE CASCADE

What problem does ON DELETE CASCADE solve?
A. Prevents orphan records in child tables
B. Prevents deletion of parent records

✅ Correct Answer: A

DATA MANIPULATION (DML)

MCQ 24: INSERT Statement Design

Why is one INSERT used per record in this script?
A. Makes the script clearer and easier to debug
B. Improves query execution speed

✅ Correct Answer: A

MCQ 25: Column Order in INSERT

Why are column names specified in the INSERT statement?
A. To ensure values match the correct columns
B. It is mandatory for all INSERT statements

✅ Correct Answer: A

MCQ 26: Missing Column Values

What happens if a column with a DEFAULT value is omitted in INSERT?
A. The default value is automatically used
B. The INSERT fails

✅ Correct Answer: A

TRANSACTIONS & CONTROL

MCQ 27: Transaction Concept

What is a transaction in SQL?
A. A group of SQL statements executed as a single unit
B. A single SELECT statement

✅ Correct Answer: A

MCQ 28: COMMIT vs ROLLBACK

What does COMMIT do in a transaction?
A. Saves all changes permanently
B. Reverses all changes

✅ Correct Answer: A

USERS & SECURITY CONCEPTS

MCQ 29: Password Storage (Conceptual)

Why are plaintext passwords unsafe in real applications?
A. They can be easily read if the database is compromised
B. They improve login speed

✅ Correct Answer: A

MCQ 30: Hashing Best Practice

What is the recommended way to store passwords?
A. Store hashed passwords
B. Store encrypted plaintext passwords

✅ Correct Answer: A

TIMESTAMP & SYSTEM GENERATED VALUES

MCQ 31: Automatic Time Tracking

Why is CURRENT_TIMESTAMP useful in tables like contacts?
A. Automatically records when data is inserted
B. Allows manual date entry only

✅ Correct Answer: A

MCQ 32: Audit Columns

Columns like created_at are mainly used for:
A. Tracking and auditing data changes
B. Sorting alphabetically

✅ Correct Answer: A

EXAM-FOCUSED APPLICATION QUESTIONS

MCQ 33: Data Consistency

Which feature ensures every image belongs to a valid animal?
A. Foreign key constraint
B. AUTO_INCREMENT

✅ Correct Answer: A

MCQ 34: Table Design Choice

Why is animal images stored in a separate table?
A. To support multiple images per animal
B. To reduce the number of records

✅ Correct Answer: A

MCQ 35: SELECT * Usage

Why is SELECT * not recommended in large production systems?
A. It retrieves unnecessary data and affects performance
B. It causes syntax errors

✅ Correct Answer: A

QUICK REVISION (VERY COMMON EXAM QUESTIONS)

MCQ 36:

DDL commands are used to:
A. Define or modify database structure
B. Insert and update data

✅ Correct Answer: A

MCQ 37:

DML commands are used to:
A. Insert, update, and retrieve data
B. Create databases

✅ Correct Answer: A

MCQ 38:

Which of the following is a DDL command?
A. CREATE TABLE
B. INSERT INTO

✅ Correct Answer: A

MCQ 39:

Which command is used to retrieve data from a table?
A. SELECT
B. DROP

✅ Correct Answer: A

MCQ 40:

Which constraint prevents duplicate primary key values?
A. PRIMARY KEY
B. DEFAULT

✅ Correct Answer: A

⭐ VERY IMPORTANT (HIGH FREQUENCY)

1. What is the purpose of CREATE DATABASE IF NOT EXISTS?

Answer:
Prevents an error by creating the database only if it does not already exist.

2. What is the use of the USE command in SQL?

Answer:
Selects the active database for executing subsequent SQL statements.

3. What does DROP TABLE IF EXISTS do?

Answer:
Deletes the table if it exists, avoiding errors when re-running the script.

4. Define PRIMARY KEY. Why is it used?

Answer:
A PRIMARY KEY uniquely identifies each record in a table and does not allow NULL or duplicate values.

5. What is the purpose of AUTO_INCREMENT?

Answer:
Automatically generates a unique value for each new record.

6. What is the use of NOT NULL constraint?

Answer:
Ensures that a column cannot have NULL (empty) values.

⭐ DATA TYPES & CONSTRAINTS (VERY COMMON)

7. What is ENUM? Give its use.

Answer:
ENUM restricts a column to a fixed set of predefined values.

8. What is the difference between VARCHAR and TEXT?

Answer:
VARCHAR stores limited-length strings, while TEXT stores longer text data.

9. What is the use of DEFAULT in a column?

Answer:
Assigns a default value when no value is provided during insertion.

10. What happens if a value is not provided for a column with DEFAULT?

Answer:
The default value is automatically inserted.

⭐ RELATIONSHIPS & KEYS (EXTREMELY IMPORTANT)

11. What is a FOREIGN KEY?

Answer:
A FOREIGN KEY is used to link two tables and enforce referential integrity.

12. What is referential integrity?

Answer:
It ensures that foreign key values always refer to existing primary key values.

13. What is the purpose of ON DELETE CASCADE?

Answer:
Automatically deletes related records in the child table when a parent record is deleted.

14. What type of relationship exists between animals and animal_images tables?

Answer:
One-to-many relationship.

15. Why are images stored in a separate table?

Answer:
To allow multiple images to be associated with a single animal.

⭐ DML COMMANDS (HIGH PROBABILITY)

16. What is the use of INSERT INTO?

Answer:
Used to add new records into a table.

17. Why are column names specified in INSERT statements?

Answer:
To ensure values are inserted into the correct columns.

18. What does SELECT * do?

Answer:
Retrieves all columns and all rows from a table.

⭐ TRANSACTIONS (COMMON THEORY QUESTION)

19. What is a transaction in SQL?

Answer:
A transaction is a group of SQL statements executed as a single unit.

20. What is the purpose of COMMIT?

Answer:
Permanently saves all changes made during a transaction.

⭐ SECURITY & BEST PRACTICES (SHORT THEORY)

21. Why should passwords not be stored in plaintext?

Answer:
They can be easily read if the database is compromised.

22. What is the recommended method for storing passwords?

Answer:
Store hashed passwords.

⭐ TIMESTAMP & SYSTEM VALUES (COMMON SHORT Q)

23. What is the use of CURRENT_TIMESTAMP?

Answer:
Automatically stores the current date and time when a record is inserted.

24. Why is created_at important in a table?

Answer:
It helps track when records were created (audit purposes).

⭐ CLASSIFICATION QUESTIONS (VERY LIKELY)

25. Define DDL commands with one example.

Answer:
DDL commands define database structure (e.g., CREATE TABLE).

26. Define DML commands with one example.

Answer:
DML commands manipulate data (e.g., INSERT INTO).

27. Which SQL command is used to retrieve data?

Answer:
SELECT

28. Which constraint ensures uniqueness of records?

Answer:
PRIMARY KEY

Below is a THOROUGH PRACTICE TEST designed for basic SQL mastery, using simple tables (1–2 columns only) while still testing all the important features you studied:
DDL, DML, constraints, keys, relationships, DEFAULT, ENUM, transactions, and SELECT.

This is ideal for exam practice and hands-on revision.

📝 BASIC SQL PRACTICE TEST

Topic: SQL Fundamentals (DDL, DML, Constraints, Transactions)
Instructions:

Answer all questions
Assume MySQL syntax
Write SQL queries where required

SECTION A: MULTIPLE CHOICE QUESTIONS (1 MARK EACH)

Q1. Which command is used to create a database?

A. CREATE DATABASE
B. CREATE TABLE

Q2. What does the USE command do?

A. Selects the active database
B. Deletes the database

Q3. Which command removes a table completely?

A. DROP TABLE
B. DELETE TABLE

Q4. Which constraint ensures that a column cannot have NULL values?

A. NOT NULL
B. UNIQUE

Q5. Which constraint uniquely identifies a record?

A. PRIMARY KEY
B. FOREIGN KEY

Q6. What is the purpose of AUTO_INCREMENT?

A. Automatically generates a unique number
B. Allows duplicate values

Q7. Which data type stores variable-length text?

A. VARCHAR
B. INT

Q8. Which command permanently saves changes?

A. COMMIT
B. ROLLBACK

Q9. Which keyword assigns a value automatically when none is provided?

A. DEFAULT
B. ENUM

Q10. Which command retrieves all rows from a table?

A. SELECT
B. INSERT

SECTION B: WRITE SQL COMMANDS (2 MARKS EACH)

Q11. Create a database named testdb only if it does not already exist.

Q12. Select the database testdb.

Q13. Create a table students with:

id → integer, primary key, auto increment
name → text, cannot be NULL

Q14. Drop the table students only if it exists.

Q15. Insert a student with name Rahul into the students table.

SECTION C: CONSTRAINTS & DEFAULT VALUES (3 MARKS)

Q16. Create a table products with:

id → primary key, auto increment
status → ENUM with values Available, Out of Stock

Default value should be Available

Q17. Insert a record into products without specifying the status.

Q18. What value will be stored in the status column? Explain.

SECTION D: FOREIGN KEY & RELATIONSHIP (3 MARKS)

Q19. Create a table departments with:

id → primary key
name → not null

Q20. Create a table employees with:

id → primary key
department_id → foreign key referencing departments(id)
Delete employees automatically if a department is deleted

Q21. What type of relationship exists between departments and employees?

SECTION E: DATA RETRIEVAL (2 MARKS)

Q22. Write a query to display all records from products.

Q23. Write a query to display all records from employees.

SECTION F: TRANSACTIONS (2 MARKS)

Q24. What is a transaction?

Q25. Write the SQL command used to save a transaction permanently.

SECTION G: SHORT THEORY QUESTIONS (1–2 MARKS)

Q26. What is the difference between DELETE and DROP?

Q27. Why is IF NOT EXISTS used in CREATE commands?

Q28. What is referential integrity?

Q29. Why should passwords be stored in hashed form?

Q30. Which SQL command is used to retrieve data from a table?

⭐ BONUS PRACTICE (OPTIONAL – VERY IMPORTANT)

Q31. Write a query to display only the name column from students.

Q32. What happens if you insert a NULL value into a NOT NULL column?

Below is a HANDS-ON SQL LAB VERSION of your practice test.
This is written exactly like a college / lab-exam worksheet, where students run commands, observe output, and understand concepts.

You can copy-paste and execute step by step in MySQL / MariaDB.

🧪 SQL HANDS-ON LAB

Topic: Basic SQL Commands & Constraints
Objective:
✔ Practice DDL, DML, constraints, keys, relationships, and transactions
✔ Use simple tables (1–2 columns) for clarity

🔹 PART 1: DATABASE SETUP

Step 1: Create Database

CREATE DATABASE IF NOT EXISTS labdb;

Step 2: Select Database

USE labdb;

🔹 PART 2: TABLE CREATION (DDL)

Task 1: Create students Table

Features tested: PRIMARY KEY, AUTO_INCREMENT, NOT NULL

CREATE TABLE students (

id INT AUTO_INCREMENT PRIMARY KEY,

name VARCHAR(50) NOT NULL

);

📌 Observation:

id auto-generates values
name cannot be NULL

Task 2: View Table Structure

DESC students;

🔹 PART 3: DATA INSERTION (DML)

Task 3: Insert Records

INSERT INTO students (name) VALUES ('Rahul');

INSERT INTO students (name) VALUES ('Anita');

Task 4: View Records

SELECT * FROM students;

Task 5: Test NOT NULL Constraint

INSERT INTO students (name) VALUES (NULL);

📌 Expected Result: ❌ Error (NOT NULL constraint)

🔹 PART 4: DEFAULT & ENUM

Task 6: Create products Table

Features tested: ENUM, DEFAULT

CREATE TABLE products (

id INT AUTO_INCREMENT PRIMARY KEY,

status ENUM('Available','Out of Stock') DEFAULT 'Available'

);

Task 7: Insert Without Status

INSERT INTO products () VALUES ();

Task 8: View Products

SELECT * FROM products;

📌 Observation:

status is automatically set to Available

🔹 PART 5: FOREIGN KEY & RELATIONSHIP

Task 9: Create departments Table

CREATE TABLE departments (

id INT PRIMARY KEY,

name VARCHAR(50) NOT NULL

);

Task 10: Create employees Table

Features tested: FOREIGN KEY, ON DELETE CASCADE

CREATE TABLE employees (

id INT PRIMARY KEY,

department_id INT,

FOREIGN KEY (department_id)

REFERENCES departments(id)

ON DELETE CASCADE

);

Task 11: Insert Parent Record

INSERT INTO departments VALUES (1, 'IT');

Task 12: Insert Child Record

INSERT INTO employees VALUES (101, 1);

Task 13: View Data

SELECT * FROM departments;

SELECT * FROM employees;

Task 14: Test ON DELETE CASCADE

DELETE FROM departments WHERE id = 1;

SELECT * FROM employees;

📌 Expected Result:

Employee record is automatically deleted

🔹 PART 6: TRANSACTIONS

Task 15: Insert Data (Without Commit)

INSERT INTO students (name) VALUES ('Temporary');

Task 16: Rollback Changes

ROLLBACK;

Task 17: Verify Rollback

SELECT * FROM students;

📌 Observation:

Inserted record is undone

Task 18: Commit Changes

INSERT INTO students (name) VALUES ('Final Student');

COMMIT;

🔹 PART 7: DATA RETRIEVAL

Task 19: Retrieve All Records

SELECT * FROM students;

Task 20: Retrieve Specific Column

SELECT name FROM students;

🔹 PART 8: CLEANUP (OPTIONAL)

DROP TABLE IF EXISTS employees;

DROP TABLE IF EXISTS departments;

DROP TABLE IF EXISTS products;

DROP TABLE IF EXISTS students;

✅ LAB LEARNING OUTCOMES

By completing this lab, you have practiced:

✔ CREATE / DROP DATABASE
✔ CREATE / DROP TABLE
✔ PRIMARY KEY & AUTO_INCREMENT
✔ NOT NULL constraint
✔ ENUM & DEFAULT
✔ FOREIGN KEY & ON DELETE CASCADE
✔ INSERT, SELECT, DELETE
✔ COMMIT & ROLLBACK

🎯 EXAM TIP

👉 In practical exams:

Always create parent table before child table
Test constraints to show understanding
Use DESC table_name; to explain structure

Below is a clean, exam-ready comparison list of the MOST IMPORTANT “X vs Y” SQL questions, written exactly in the format examiners expect.
Each item includes short, clear answers suitable for 2–5 mark questions.

1. DROP vs DELETE

Feature	DROP	DELETE
Type	DDL command	DML command
Purpose	Removes the table completely	Removes rows from a table
Data	All data is lost	Selected or all rows can be removed
Structure	Table structure is deleted	Table structure remains
WHERE clause	❌ Not allowed	✅ Allowed
Rollback	❌ Cannot be rolled back	✅ Can be rolled back (before COMMIT)

Example:

DROP TABLE students;

DELETE FROM students WHERE id = 1;

2. VARCHAR vs CHAR

Feature	VARCHAR	CHAR
Length	Variable length	Fixed length
Storage	Uses only required space	Uses full allocated space
Performance	Slightly slower	Faster
Best for	Names, addresses	Fixed-size data (gender, codes)

Example:

name VARCHAR(50);

gender CHAR(1);

3. DELETE vs TRUNCATE

Feature	DELETE	TRUNCATE
Type	DML	DDL
WHERE clause	✅ Allowed	❌ Not allowed
Rollback	✅ Possible	❌ Not possible
Speed	Slower	Faster
Table structure	Remains	Remains

4. PRIMARY KEY vs FOREIGN KEY

Feature	PRIMARY KEY	FOREIGN KEY
Purpose	Uniquely identifies a record	Links two tables
Duplicate values	❌ Not allowed	✅ Allowed
NULL values	❌ Not allowed	✅ Allowed
Count per table	Only one	Multiple allowed

5. WHERE vs HAVING

Feature	WHERE	HAVING
Used with	Rows	Groups
Aggregate functions	❌ Not allowed	✅ Allowed
Execution	Before GROUP BY	After GROUP BY

6. DDL vs DML

Feature	DDL	DML
Full form	Data Definition Language	Data Manipulation Language
Purpose	Defines structure	Manipulates data
Examples	CREATE, DROP	INSERT, UPDATE
Rollback	❌ Not possible	✅ Possible

7. INT vs BIGINT

Feature	INT	BIGINT
Storage	4 bytes	8 bytes
Range	Smaller	Very large
Usage	IDs, age	Large counters

8. NULL vs NOT NULL

Feature	NULL	NOT NULL
Meaning	No value	Value required
Insert allowed	Yes	No
Usage	Optional fields	Mandatory fields

9. DEFAULT vs AUTO_INCREMENT

Feature	DEFAULT	AUTO_INCREMENT
Purpose	Assigns a fixed value	Generates increasing numbers
Used for	Status, flags	Primary keys
Manual override	Allowed	Usually not

10. COMMIT vs ROLLBACK

Feature	COMMIT	ROLLBACK
Purpose	Saves changes	Cancels changes
Effect	Permanent	Temporary undo
Usage	End of transaction	Error handling

🔑 EXAM TIP (VERY IMPORTANT)

👉 For “Differentiate between” questions:

Draw table format
Write at least 4 points
Add one example → guaranteed full marks

Below are PRACTICAL-EXAM VIVA QUESTIONS based strictly on basic SQL commands, exactly the type examiners ask during lab viva.
Each question has a short, clear answer that you can memorize and speak confidently.

🎤 SQL PRACTICAL-EXAM VIVA QUESTIONS & ANSWERS

🔹 BASIC SQL & DATABASE

1. What is SQL?

Answer:
SQL (Structured Query Language) is used to create, manage, and manipulate data in relational databases.

2. What is a database?

Answer:
A database is an organized collection of related data stored electronically.

3. What is the use of CREATE DATABASE?

Answer:
It is used to create a new database.

4. Why do we use the USE command?

Answer:
To select the database on which SQL commands will be executed.

5. What is the difference between database and table?

Answer:
A database contains tables, while a table stores actual data in rows and columns.

🔹 TABLE & DDL COMMANDS

6. What is DDL?

Answer:
DDL (Data Definition Language) is used to define or modify database structure.

7. Name any two DDL commands.

Answer:
CREATE, DROP.

8. What does DROP TABLE do?

Answer:
It deletes the table structure along with all data permanently.

9. What is the use of IF NOT EXISTS?

Answer:
It prevents errors if the table or database already exists.

10. What is the difference between DROP and DELETE?

Answer:
DROP removes the table completely, while DELETE removes records from a table.

🔹 DATA TYPES & CONSTRAINTS

11. What is a data type?

Answer:
A data type defines the kind of value a column can store.

12. What is VARCHAR?

Answer:
VARCHAR stores variable-length character data.

13. Difference between VARCHAR and CHAR?

Answer:
VARCHAR uses variable space, CHAR uses fixed space.

14. What is NOT NULL?

Answer:
It ensures that a column cannot store NULL values.

15. What is DEFAULT?

Answer:
It assigns a default value when no value is provided.

🔹 KEYS & RELATIONSHIPS (VERY IMPORTANT)

16. What is a PRIMARY KEY?

Answer:
A primary key uniquely identifies each record in a table.

17. Can a table have more than one primary key?

Answer:
No, a table can have only one primary key.

18. What is a FOREIGN KEY?

Answer:
A foreign key is used to link two tables.

19. What is referential integrity?

Answer:
It ensures that foreign key values exist in the parent table.

20. What is ON DELETE CASCADE?

Answer:
It automatically deletes child records when a parent record is deleted.

🔹 DML COMMANDS

21. What is DML?

Answer:
DML (Data Manipulation Language) is used to insert, update, and delete data.

22. Name any two DML commands.

Answer:
INSERT, SELECT.

23. What does INSERT INTO do?

Answer:
It adds new records to a table.

24. What does SELECT * do?

Answer:
It retrieves all rows and columns from a table.

25. What is the use of WHERE clause?

Answer:
It filters records based on a condition.

🔹 TRANSACTIONS (COMMON VIVA AREA)

26. What is a transaction?

Answer:
A transaction is a group of SQL statements executed as one unit.

27. What is COMMIT?

Answer:
COMMIT permanently saves the changes made.

28. What is ROLLBACK?

Answer:
ROLLBACK undoes changes made before COMMIT.

29. Can DROP be rolled back?

Answer:
No, DROP cannot be rolled back.

🔹 PRACTICAL SCENARIO QUESTIONS

30. Why should parent tables be created before child tables?

Answer:
Because foreign keys depend on primary keys of parent tables.

31. What happens if you insert NULL into a NOT NULL column?

Answer:
An error occurs.

32. Why do we use AUTO_INCREMENT?

Answer:
To automatically generate unique values for primary keys.

33. Why are passwords not stored in plaintext?

Answer:
For security reasons, to prevent misuse if data is leaked.

34. What is ENUM?

Answer:
ENUM restricts a column to a fixed set of values.

35. What is the advantage of using separate tables for related data?

Answer:
It reduces data redundancy and improves data integrity.

⭐ FINAL VIVA TIPS (VERY IMPORTANT)

✔ Answer short and confident
✔ Use keywords: “uniquely identifies”, “referential integrity”, “automatically”
✔ If stuck → explain using example table names

If you want next:

🎯 Top 20 guaranteed viva questions
🧠 One-line memory answers
⏱ Mock viva (I ask, you answer)
📄 Printable viva cheat sheet

Just tell me 👍

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