🚀 Web Development Interview Questions with Answers — Part 6: Database

🧠 131. What is SQL?

SQL stands for: 👉 Structured Query Language

It is used to manage and manipulate relational databases.

Uses:

• Store data

• Retrieve data

• Update records

• Delete records

Example:

SELECT * FROM users;

🧠 132. Difference Between SQL and NoSQL

SQL : Relational database : Uses tables : Structured schema

NoSQL : Non-relational database : Uses collections/documents : Flexible schema

Examples:

• SQL → MySQL

• NoSQL → MongoDB

🧠 133. What is Primary Key?

Primary key uniquely identifies each record in a table.

Features:

✅ Unique

✅ Cannot be NULL

Example:

CREATE TABLE users (

id INT PRIMARY KEY,

name VARCHAR(50)

);

🧠 134. What is Foreign Key?

Foreign key creates relationship between two tables.

Example:

CREATE TABLE orders (

order_id INT,

user_id INT,

FOREIGN KEY (user_id) REFERENCES users(id)

);

🧠 135. What is Normalization?

Normalization organizes database to reduce redundancy.

Normal Forms:

• 1NF

• 2NF

• 3NF

Benefits:

✅ Reduced duplication

✅ Better consistency

✅ Improved integrity

🧠 136. What are Joins in SQL?

Joins combine data from multiple tables.

Types:

• INNER JOIN

• LEFT JOIN

• RIGHT JOIN

• FULL JOIN

Example:

SELECT users.name, orders.amount

FROM users

INNER JOIN orders

ON users.id = orders.user_id;

🧠 137. Difference Between INNER JOIN and LEFT JOIN

INNER JOIN : Returns matching rows only

LEFT JOIN : Returns all left table rows

Example:

SELECT * FROM users

LEFT JOIN orders

ON users.id = orders.user_id;

🧠 138. What is Indexing?

Index improves database query performance.

Benefits:

✅ Faster searches

✅ Faster filtering

Example:

CREATE INDEX idx_name

ON users(name);

🧠 139. What is Aggregate Function?

Aggregate functions perform calculations on multiple rows.

Common Functions:

• COUNT()

• SUM()

• AVG()

• MIN()

• MAX()

Example:

SELECT COUNT(*) FROM users;

🧠 140. Difference Between DELETE, DROP, and TRUNCATE

DELETE : Removes rows : Can use WHERE

DROP : Removes table : Deletes structure

TRUNCATE : Removes all rows : Faster than DELETE

Example:

DELETE FROM users WHERE id = 1;

🧠 141. What is MongoDB?

MongoDB is a NoSQL database that stores data in JSON-like documents.

Features:

✅ Flexible schema

✅ High scalability

✅ Fast performance

Example Document:

{

"name": "Deepak",

"age": 25

}

🧠 142. Difference Between MongoDB and MySQL

MongoDB : NoSQL : Flexible schema : Document-based

MySQL : SQL : Fixed schema : Table-based

🧠 143. What is Schema?

Schema defines structure of database.

Example:

CREATE TABLE users (

id INT,

name VARCHAR(50)

);

🧠 144. What is ORM?

ORM stands for: 👉 Object Relational Mapping

ORM allows interaction with database using programming language objects.

Benefits:

✅ Easier queries

✅ Cleaner code

✅ Faster development

🧠 145. What is Sequelize?

Sequelize is an ORM for Node.js.

Example:

User.findAll();