What are all the difference between SQL and No SQL ?

Overview

SQL (Structured Query Language) and NoSQL (Not Only SQL) are two fundamentally different approaches to storing and retrieving data.

Core Differences

SQL Databases

SQL databases store data in tables with a predefined schema. Relationships between data are maintained using foreign keys and resolved with JOIN queries.

Popular SQL Databases:

• PostgreSQL
• MySQL
• SQLite (used in Flutter via
  textCopy

  sqflite

  )
• Microsoft SQL Server

Example (SQLite in Flutter)

sqlCopy
-- Create table
CREATE TABLE orders (
  id INTEGER PRIMARY KEY,
  user_id INTEGER,
  total REAL,
  FOREIGN KEY (user_id) REFERENCES users(id)
);

-- Join query
SELECT users.name, orders.total
FROM users
JOIN orders ON users.id = orders.user_id;

When to Use SQL

• Data has clear relationships (users → orders → products)
• You need complex queries with filters, sorts, and joins
• Data integrity is critical (e.g., banking, ERP systems)
• Schema is unlikely to change frequently

NoSQL Databases

NoSQL databases store data in flexible formats — documents, key-value pairs, wide columns, or graphs. There is no fixed schema, so each record can have different fields.

Types of NoSQL:

Example (Firebase Firestore)

dartCopy
// No fixed schema — each document can have different fields
await FirebaseFirestore.instance.collection('users').add({
  'name': 'Alice',
  'age': 28,
  'interests': ['flutter', 'dart'], // Array — not easy in SQL
  'address': {                       // Nested object
    'city': 'Chennai',
    'country': 'India',
  }
});

When to Use NoSQL

• Data structure varies between records
• You need to scale to millions of users horizontally
• Fast reads/writes are more important than complex queries
• Real-time updates (e.g., chat apps, live dashboards)
• Rapid development with changing requirements

Performance

In Flutter Context

sqflite

Hive

Isar

Firebase Firestore

Supabase

Summary: Choose SQL when your data is highly relational and structured. Choose NoSQL when you need flexibility, scale, and speed.