What Is a Database and How Do Apps Use Them?

Every app that stores information uses a database. Your social media account, your order history, your saved preferences — all of that lives in a database somewhere. As a developer, understanding what databases are and how apps use them is fundamental.

What Is a Database?

A database is an organised collection of data that can be easily stored, retrieved, and updated. Think of it as a highly structured, queryable spreadsheet. Instead of a flat file, you get a system optimised for fast reads and writes at scale.

SQL Databases (Relational)

SQL databases store data in tables with rows and columns, like a spreadsheet. Tables relate to each other via keys. Examples: PostgreSQL, MySQL, SQLite.

-- A users table
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  name VARCHAR(100),
  email VARCHAR(255) UNIQUE,
  created_at TIMESTAMP DEFAULT NOW()
);

-- Find a user by email
SELECT * FROM users WHERE email = 'kai@kaiko.dev';

SQL databases are great for structured data with clear relationships — e-commerce (orders relate to users relate to products), banking, and most traditional web apps.

NoSQL Databases

NoSQL databases store data in flexible formats — documents, key-value pairs, graphs. Examples: MongoDB (documents), Redis (key-value), Elasticsearch (search).

// A MongoDB document — no rigid schema required
{
  "_id": "user_001",
  "name": "Kaikobud",
  "skills": ["Python", "Go", "Docker"],
  "address": {
    "city": "Dhaka",
    "country": "Bangladesh"
  }
}

NoSQL is great for flexible schemas, high write volume, and data that doesn’t fit neatly into tables.

How Apps Use Databases

The flow is always the same:

1. User performs an action (submits a form, clicks a button)
2. The server receives the request
3. The server queries the database (read or write)
4. The database returns a result
5. The server sends a response to the user

The app never talks to the database directly from the browser — only the server does. This is important for security.

Conclusion

A database is where your app’s data lives. SQL databases for structured, relational data; NoSQL for flexibility and scale. As a backend developer, you’ll spend a lot of time writing queries, designing schemas, and thinking about how data flows through your application. Start with PostgreSQL — it’s excellent and free.

Read next: Connecting Python to PostgreSQL with psycopg2

External resource: PostgreSQL Official Documentation