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100 lines
3.2 KiB
Markdown
100 lines
3.2 KiB
Markdown
# PostgreSQL — Patterns e Anti-patterns
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> Conexão | Schemas | JSONB | Junções | Window Functions | Migrações | EXPLAIN
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## Comandos Rápidos
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```bash
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psql "postgresql://user:pass@host:5432/db?sslmode=require"
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psql -h localhost -U user -d db -c "SELECT NOW();"
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psql -h host -U user -d db -f migration.sql
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```
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## Schema Design
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```sql
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-- UUIDs para PK distribuído-friendly (ativar extensão primeiro)
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CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
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CREATE TABLE users (
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id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
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email TEXT NOT NULL UNIQUE,
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name TEXT NOT NULL,
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role TEXT NOT NULL DEFAULT 'user' CHECK(role IN ('user','admin','moderator')),
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created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
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);
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-- Auto-update updated_at
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CREATE OR REPLACE FUNCTION update_modified_column()
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RETURNS TRIGGER AS $$ BEGIN NEW.updated_at = NOW(); RETURN NEW; END; $$ LANGUAGE plpgsql;
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CREATE TRIGGER update_users_modtime BEFORE UPDATE ON users
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FOR EACH ROW EXECUTE FUNCTION update_modified_column();
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-- Enum
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CREATE TYPE order_status AS ENUM ('pending','paid','shipped','cancelled');
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```
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## JSONB Ops
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```sql
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INSERT INTO orders (metadata) VALUES ('{"source":"web","items":[{"sku":"A1","qty":2}]}'::jsonb);
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SELECT * FROM orders WHERE metadata->>'source' = 'web';
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SELECT * FROM orders WHERE metadata->'items' @> '[{"sku":"A1"}]'::jsonb; -- @> contains
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UPDATE orders SET metadata = jsonb_set(metadata, '{source}', '"mobile"') WHERE id = '...';
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SELECT metadata->>'coupon' AS coupon, COUNT(*) FROM orders GROUP BY 1;
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```
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## Indexes
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```sql
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CREATE UNIQUE INDEX idx_users_email ON users(email); -- único
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CREATE INDEX idx_orders_user_created ON orders(user_id, created_at); -- composto
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CREATE INDEX idx_orders_active ON orders(user_id, created_at) -- parcial
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WHERE status NOT IN ('delivered','cancelled');
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CREATE INDEX idx_orders_metadata ON orders USING GIN(metadata); -- GIN para JSONB
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```
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## Window Functions
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```sql
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SELECT date, revenue,
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SUM(revenue) OVER (ORDER BY date) AS cumulative_revenue, -- running total
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AVG(revenue) OVER (PARTITION BY region) AS avg_by_region,
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RANK() OVER (ORDER BY revenue DESC) AS ranking
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FROM daily_sales;
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```
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## JOINS Rápidos
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```sql
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-- LEFT JOIN pega todos os usuários, mesmo sem pedidos
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SELECT u.name, COUNT(o.id) AS order_count, COALESCE(SUM(o.total), 0) AS total_spent
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FROM users u LEFT JOIN orders o ON o.user_id = u.id
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GROUP BY u.id, u.name HAVING COUNT(o.id) > 5 ORDER BY total_spent DESC;
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```
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## CTEs (WITH)
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```sql
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WITH active_users AS (
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SELECT id, name FROM users WHERE active = true
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)
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SELECT au.name, COUNT(o.id) AS orders
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FROM active_users au LEFT JOIN orders o ON o.user_id = au.id
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GROUP BY au.name;
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```
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## EXPLAIN ANALYZE (antes de otimizar)
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```bash
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EXPLAIN ANALYZE SELECT ... -- SEMPRE antes de criar um índice
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```
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## Migrations — Padrão
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```bash
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# Criar timestamped
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psql -h host -U user -d db -f migrations/2025-06-19_add_field.sql
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```
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## Checklist de Otimização
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- [ ] `EXPLAIN ANALYZE` antes e depois de cada mudança
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- [ ] Medir tempo de resposta alvo antes de otimizar
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- [ ] Evitar `SELECT *` em produção
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- [ ] Criar índices para colunas em `WHERE`, `JOIN`, `ORDER BY`
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- [ ] Índice parcial para subconjuntos pequenos
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- [ ] Partial/Paginado para tabelas grandes
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