NoSQL Databases

NoSQL databases store data in non-relational formats — documents, key-value pairs, graphs, or columns.

Syntax

COMPUTER-SCIENCE

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# Document: MongoDB
{ "name": "Alice", "scores": [95, 87] }

# Key-Value: Redis
SET user:1 "Alice"
GET user:1

# Graph: Neo4j
(Alice)-[:FRIENDS_WITH]->(Bob)

Document Database Concept

JAVASCRIPT

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// MongoDB-style document
const user = {
    _id: "507f1f77bcf86cd799439011",
    name: "Alice",
    email: "alice@example.com",
    address: {
        city: "New York",
        zip: "10001"
    },
    hobbies: ["reading", "coding"],
    createdAt: new Date()
};

// Query concept
const query = { "address.city": "New York" };
console.log("Document:", JSON.stringify(user, null, 2));
console.log("Query:", query);

Try It Yourself

Practice

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Exercise

When should you use NoSQL over SQL?

Answer

When you need flexible schemas, horizontal scaling, or work with unstructured data.

Quick Quiz

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Which is a document database?

MySQL

PostgreSQL

MongoDB

Redis

MongoDB is a document database that stores JSON-like documents.

Retry Quiz

Interview Questions

What is eventual consistency?

A consistency model where all nodes will eventually have the same data, but not immediately after a write. Common in distributed NoSQL systems.

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Relational Databases

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