What are all the difference between relational and non-relational databases ?

Overview

Relational and non-relational databases differ in how they organize, store, and relate data. This is the foundation of the SQL vs NoSQL debate.

Key Differences

Relational Databases

Data is organized into tables with rows and columns. Relationships are enforced through foreign keys and retrieved with JOIN statements.

Examples: MySQL, PostgreSQL, SQLite, Oracle DB

sqlCopy
-- Users table
CREATE TABLE users (
  id INTEGER PRIMARY KEY,
  name TEXT NOT NULL,
  email TEXT UNIQUE NOT NULL
);

-- Orders table with a foreign key relationship
CREATE TABLE orders (
  id INTEGER PRIMARY KEY,
  user_id INTEGER NOT NULL,
  amount REAL,
  FOREIGN KEY (user_id) REFERENCES users(id)
);

-- JOIN to get related data
SELECT u.name, o.amount
FROM users u
JOIN orders o ON u.id = o.user_id
WHERE u.id = 1;

Pros

• ✅ Data integrity guaranteed
• ✅ Avoids data duplication (normalization)
• ✅ Powerful complex queries
• ✅ ACID transactions

Cons

• ❌ Rigid schema — hard to change
• ❌ Harder to scale horizontally
• ❌ Slower for very large datasets

Non-Relational Databases

Data is stored in flexible formats — typically as documents (JSON/BSON), key-value pairs, or graphs. No fixed schema required.

Examples: Firebase Firestore, MongoDB, Redis, Hive, Cassandra

dartCopy
// Firestore: Data stored as nested documents (no foreign keys needed)
final user = {
  'id': '001',
  'name': 'Alice',
  'email': 'alice@example.com',
  'orders': [               // Embedded directly in the document
    {'item': 'Book', 'amount': 300},
    {'item': 'Pen', 'amount': 50},
  ]
};

await FirebaseFirestore.instance
    .collection('users')
    .doc('001')
    .set(user);

Pros

• ✅ Flexible schema — easy to evolve
• ✅ Scales horizontally (millions of records)
• ✅ Faster reads for document-based access
• ✅ Natural fit for JSON APIs and mobile apps

Cons

• ❌ Data duplication is common
• ❌ Complex queries are harder
• ❌ Weaker consistency guarantees

Real-World Analogy

Which to Use in Flutter?

SharedPreferences

sqflite

Drift

Firebase Firestore

Supabase

Hive

Isar

Rule of Thumb: If your data has clear relationships and needs integrity → Relational. If your data is flexible and needs to scale → Non-Relational.