SQL Basics
Learn the fundamentals of Structured Query Language (SQL), the most widely used language for relational databases.
SELECT Statement
Retrieve data from one or more tables.
SELECT column1, column2
FROM users
WHERE age > 18
ORDER BY created_at DESC;INSERT Statement
INSERT INTO users (name, email, age)
VALUES ('Jane Doe', 'jane@example.com', 28);NoSQL Overview
NoSQL databases provide flexible schemas and horizontal scaling. Here are three popular types.
Document Stores (MongoDB)
db.users.insertOne({
name: "John Smith",
email: "john@example.com",
tags: ["admin", "beta"]
});Key‑Value Stores (Redis)
SET session:12345 "user_id=7"Column Family (Cassandra)
INSERT INTO users (id, name, email)
VALUES (uuid(), 'Alice', 'alice@example.com');Object‑Relational Mapping (ORM)
ORMs let you interact with databases using native language objects.
Example with Sequelize (Node.js)
const { Model, DataTypes } = require('sequelize');
class User extends Model {}
User.init({
name: DataTypes.STRING,
email: DataTypes.STRING
}, { sequelize, modelName: 'user' });
await User.create({ name: 'Bob', email: 'bob@example.com' });Performance Tips
- Index wisely: Index columns used in WHERE, JOIN, ORDER BY.
- Avoid SELECT * unless you truly need all columns.
- Batch writes: Group inserts/updates to reduce round trips.
- Monitor queries: Use EXPLAIN plans to detect slow operations.