# MySQL — Patterns e Anti-patterns

> Conexão | Schemas | JSON | InnoDB | Otimização

## Comandos Rápidos
```bash
mysql -h localhost -u root -p mydb
mysql -h host -u user -p -e "SELECT NOW();" mydb
mysql -h host -u user -p mydb < migration.sql
```

## Schema Design
```sql
CREATE TABLE users (
    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    email VARCHAR(255) NOT NULL UNIQUE,
    name VARCHAR(255) NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
```
> **SEMPRE** `ENGINE=InnoDB` — transações, FK, row-level locking. `utf8mb4` — suporta emoji e acentos completos.

## JSON Ops
```sql
CREATE TABLE orders (
    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    metadata JSON,
    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
);

SELECT * FROM orders WHERE JSON_EXTRACT(metadata, '$.source') = 'web';
-- Shorthand (MySQL 8+):
SELECT * FROM orders WHERE metadata->>'$.source' = 'web';
```

## Indexes
```sql
-- Index composto
CREATE INDEX idx_orders_user_id ON orders(user_id);

-- Índice parcial (simulado com generated column + índice)
ALTER TABLE orders ADD COLUMN is_active TINYINT(1) 
  GENERATED ALWAYS AS (status != 'cancelled') STORED;
CREATE INDEX idx_orders_active ON orders(is_active);
```

## Joins e Agregações
```sql
SELECT u.name, o.total, o.status
FROM users u
INNER JOIN orders o ON o.user_id = u.id
WHERE o.created_at > '2026-01-01'
ORDER BY o.total DESC
LIMIT 10;

SELECT status, COUNT(*) AS cnt, SUM(total) AS revenue
FROM orders GROUP BY status HAVING cnt > 5;
```

## Diferenças principais vs PostgreSQL
| Aspecto | MySQL | PostgreSQL |
|---------|-------|-------------|
| Auto-increment | `AUTO_INCREMENT` | `SERIAL` / `IDENTITY` |
| UUID padrão | Requer plugin (não padrão) | `uuid-ossp` built-in |
| JSON | `JSON` type (baixa performance em queries) | `JSONB` indexável |
| CTEs | Suportado (MySQL 8+) | Nativo desde sempre |
| Window Functions | MySQL 8+ | Nativo |
| Transactions | InnoDB obrigatório | Sempre |
| Null-safe join | `<=>` (spaceship operator) | `IS NOT DISTINCT FROM` |