SQL

When to Use

• Relational data modeling
• Complex queries and aggregations
• Data integrity enforcement (ACID)
• Standardized data access

Quick Start

-- Create Table
CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100) UNIQUE
);

-- Insert Data
INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com');

-- Query Data
SELECT * FROM users WHERE name = 'Alice';

Core Concepts

DDL (Data Definition Language)

DML (Data Manipulation Language)

Joins

• INNER JOIN: Matches in both tables.
• LEFT JOIN: All from left, matches from right.

Best Practices

• Use parameterized queries (prevent SQL Injection)
• Index columns used in WHERE and JOIN clauses
• Use transactions for atomic operations

• Use

  SELECT *

  in production (fetch only what you need)
• Store logic in triggers if possible (hard to debug)
• Ignore execution plans for slow queries

References

• PostgreSQL Documentation