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mediumSystem Design

When would you choose SQL vs NoSQL?

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01

Understand the problem

Compare relational and NoSQL databases.

databasesql-nosql
02

Attempt it yourself

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03

Study the solution

SQL vs. NoSQL: When Would You Choose Which?

Target Audience: Junior & Senior Software Engineers preparing for System Design Interviews — no prior system design knowledge assumed. Difficulty: Easy to Medium

How to read this doc: Every concept is explained in plain language first. Right after, you'll se

Solution ready — 2 min read

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04

Read the code

Relational schema (SQL)
-- Normalized: users and orders in separate tables, joined by user_id
CREATE TABLE users (
  id    BIGINT PRIMARY KEY,
  email TEXT UNIQUE NOT NULL,
  name  TEXT NOT NULL
);

CREATE TABLE orders (
  id          BIGINT PRIMARY KEY,
  user_id     BIGINT NOT NULL REFERENCES users(id),
  total_cents INT    NOT NULL,
  created_at  TIMESTAMPTZ DEFAULT now()
);

-- Read needs a join:
SELECT u.name, o.total_cents
FROM orders o JOIN users u ON u.id = o.user_id
WHERE u.email = 'ada@example.com';
Document model (NoSQL)
Run Playground
// Same data denormalized into ONE document — no joins, one read.
{
  "_id": "user_42",
  "email": "ada@example.com",
  "name": "Ada",
  "orders": [
    { "id": "o_1", "totalCents": 4999, "createdAt": "2024-01-04T10:00:00Z" },
    { "id": "o_2", "totalCents": 1200, "createdAt": "2024-02-11T08:30:00Z" }
  ]
}
05

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