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SQL (Structured Query Language) is the standard language for managing and manipulating relational databases.
This page is currently being developed. Check back soon for comprehensive SQL documentation.

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Overview

SQL is used to:
  • Query data from databases
  • Insert, update, and delete records
  • Create and modify database structures
  • Control access to data
  • Manage transactions

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Coming Soon

This documentation will cover:

Basic Queries

SELECT statements, filtering with WHERE, sorting with ORDER BY

Data Manipulation

INSERT, UPDATE, DELETE operations and best practices

Joins & Relations

INNER JOIN, LEFT JOIN, RIGHT JOIN, and complex relationships

Advanced Topics

Subqueries, CTEs, window functions, and optimization

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Quick Reference

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Basic SELECT

Query all columns
SELECT * FROM users;
Query specific columns
SELECT name, email FROM users;
Filter results
SELECT * FROM users WHERE age > 18;
Sort results
SELECT * FROM users ORDER BY name ASC;

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Data Manipulation

Insert data
INSERT INTO users (name, email, age) 
VALUES ('John Doe', '[email protected]', 25);
Update data
UPDATE users 
SET email = '[email protected]' 
WHERE id = 1;
Delete data
DELETE FROM users WHERE id = 1;

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Table Operations

Create table
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  name VARCHAR(100) NOT NULL,
  email VARCHAR(255) UNIQUE NOT NULL,
  age INTEGER,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
Alter table
ALTER TABLE users ADD COLUMN phone VARCHAR(20);
Drop table
DROP TABLE IF EXISTS users;

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Common Patterns

Count all records
SELECT COUNT(*) FROM users;
Count with condition
SELECT COUNT(*) FROM users WHERE age > 18;
Group by and count
SELECT country, COUNT(*) as user_count 
FROM users 
GROUP BY country;
Exact match
SELECT * FROM users WHERE name = 'John Doe';
Pattern matching
SELECT * FROM users WHERE name LIKE 'John%';
Case-insensitive search (PostgreSQL)
SELECT * FROM users WHERE name ILIKE '%john%';

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Database-Specific Dialects

SQL syntax can vary slightly between database systems (PostgreSQL, MySQL, SQLite, SQL Server). Always check your specific database documentation for exact syntax.
PostgreSQL is a powerful, open-source object-relational database system.
PostgreSQL-specific features
-- Serial auto-increment
CREATE TABLE users (
  id SERIAL PRIMARY KEY
);

-- JSON support
SELECT data->>'name' FROM users;

-- Array types
SELECT * FROM posts WHERE 'sql' = ANY(tags);

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Best Practices

Use Indexes

Create indexes on frequently queried columns to improve performance.

Avoid SELECT *

Select only the columns you need to reduce data transfer and improve performance.

Use Transactions

Wrap related operations in transactions to ensure data consistency.

Parameterize Queries

Always use parameterized queries to prevent SQL injection attacks.

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Security

Never concatenate user input directly into SQL queries. This opens your application to SQL injection attacks.
// DON'T DO THIS!
const query = `SELECT * FROM users WHERE email = '${userInput}'`;

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Resources

This page will be expanded with more comprehensive examples, advanced queries, performance optimization tips, and database-specific features. Stay tuned for updates!

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