# Referencia Rápida de PostgreSQL

*Tablas, consultas, joins, índices, JSON, roles*

> Source: PostgreSQL Documentation (postgresql.org/docs) · MIT

## Conexión

### Línea de Comandos

```
psql -U postgres
psql -h localhost -p 5432 -U user -d mydb
psql "postgresql://user:pass@host:5432/mydb"
```

### Metacomandos de psql

| Command | Description |
|---------|-------------|
| `\l` | Listar bases de datos |
| `\c dbname` | Conectar a la base de datos |
| `\dt` | Listar tablas |
| `\d tablename` | Describir la estructura de la tabla |
| `\dn` | Listar esquemas |
| `\du` | Listar roles |
| `\q` | Salir de psql |
| `\i file.sql` | Ejecutar archivo SQL |

## Tablas y Esquemas

### Crear Tabla

```
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  name VARCHAR(100) NOT NULL,
  email TEXT UNIQUE,
  created_at TIMESTAMPTZ DEFAULT NOW()
);
```

### Operaciones de Esquema

```
CREATE SCHEMA app;
CREATE TABLE app.users (id SERIAL PRIMARY KEY);
SET search_path TO app, public;
DROP SCHEMA app CASCADE;
```

### Modificar Tabla

```
ALTER TABLE users ADD COLUMN age INT;
ALTER TABLE users ALTER COLUMN name TYPE TEXT;
ALTER TABLE users DROP COLUMN age;
ALTER TABLE users RENAME TO customers;
```

## Tipos de Datos

### Numéricos

| Command | Description |
|---------|-------------|
| `INTEGER / INT` | Entero de 4 bytes |
| `BIGINT` | Entero de 8 bytes |
| `SERIAL` | Entero auto-incremental |
| `NUMERIC(p,s)` | Numérico exacto (ej., NUMERIC(10,2)) |
| `REAL / DOUBLE PRECISION` | Punto flotante (4 / 8 bytes) |
| `BOOLEAN` | true / false / null |

### Cadenas y Binarios

| Command | Description |
|---------|-------------|
| `TEXT` | Texto variable ilimitado |
| `VARCHAR(n)` | Texto variable hasta n caracteres |
| `CHAR(n)` | Texto de longitud fija |
| `BYTEA` | Datos binarios |
| `UUID` | Identificador único universal de 128 bits |

### Fecha, JSON y Array

| Command | Description |
|---------|-------------|
| `DATE` | Fecha del calendario |
| `TIMESTAMPTZ` | Timestamp con zona horaria |
| `INTERVAL` | Intervalo de tiempo (ej., '2 days') |
| `JSONB` | JSON binario (indexable) |
| `INT[] / TEXT[]` | Tipos de array |

## Consultas

### Insertar

```
INSERT INTO users (name, email)
VALUES ('Alice', 'alice@example.com')
RETURNING id;

INSERT INTO users (name, email) VALUES
('Bob', 'bob@ex.com'),
('Carol', 'carol@ex.com');
```

### Seleccionar

```
SELECT * FROM users WHERE id = 1;
SELECT name, email FROM users
ORDER BY name LIMIT 10 OFFSET 20;
```

### Actualizar

```
UPDATE users SET email = 'new@ex.com'
WHERE id = 1 RETURNING *;
```

### Upsert

```
INSERT INTO users (email, name)
VALUES ('a@ex.com', 'Alice')
ON CONFLICT (email) DO UPDATE
SET name = EXCLUDED.name;
```

### Eliminar

```
DELETE FROM users WHERE id = 1 RETURNING *;
TRUNCATE TABLE users RESTART IDENTITY;
```

## Joins y Subconsultas

### Tipos de Join

| Command | Description |
|---------|-------------|
| `INNER JOIN` | Filas coincidentes en ambas tablas |
| `LEFT JOIN` | Todas las filas izquierdas + coincidencias derechas |
| `RIGHT JOIN` | Todas las filas derechas + coincidencias izquierdas |
| `FULL OUTER JOIN` | Todas las filas de ambas tablas |
| `CROSS JOIN` | Producto cartesiano |
| `LATERAL JOIN` | Subconsulta que referencia la fila exterior |

### CTE (Expresión de Tabla Común)

```
WITH active AS (
  SELECT * FROM users WHERE active = true
)
SELECT a.name, o.total
FROM active a
JOIN orders o ON a.id = o.user_id;
```

### Subconsulta

```
SELECT name FROM users
WHERE id IN (
  SELECT user_id FROM orders
  WHERE total > 100
);
```

## Índices

### Crear y Eliminar

```
CREATE INDEX idx_name ON users(name);
CREATE UNIQUE INDEX idx_email ON users(email);
CREATE INDEX idx_gin ON posts USING GIN(tags);
DROP INDEX idx_name;
```

### Tipos de Índice

| Command | Description |
|---------|-------------|
| `B-tree` | Predeterminado, ideal para =, <, >, BETWEEN |
| `Hash` | Solo comparaciones de igualdad |
| `GIN` | Invertido generalizado — arrays, JSONB, texto completo |
| `GiST` | Búsqueda generalizada — geométrico, rangos |
| `BRIN` | Rango de bloques — tablas grandes ordenadas |

### Análisis de Consulta

```
EXPLAIN ANALYZE
SELECT * FROM users WHERE name = 'Alice';
```

## Funciones y Procedimientos

### Función SQL

```
CREATE FUNCTION active_count()
RETURNS INTEGER AS $$
  SELECT COUNT(*)::INT FROM users
  WHERE active = true;
$$ LANGUAGE sql;
SELECT active_count();
```

### Función PL/pgSQL

```
CREATE FUNCTION greet(name TEXT)
RETURNS TEXT AS $$
BEGIN
  RETURN 'Hello, ' || name;
END;
$$ LANGUAGE plpgsql;
```

### Funciones Integradas Útiles

| Command | Description |
|---------|-------------|
| `NOW() / CURRENT_TIMESTAMP` | Timestamp actual con zona horaria |
| `AGE(ts1, ts2)` | Intervalo entre timestamps |
| `COALESCE(a, b)` | Primer valor no nulo |
| `NULLIF(a, b)` | NULL si a = b |
| `GENERATE_SERIES(1,10)` | Generar filas de valores secuenciales |
| `STRING_AGG(col, ',')` | Concatenar valores con separador |

## Roles y Permisos

### Gestión de Roles

```
CREATE ROLE app LOGIN PASSWORD 'secret';
ALTER ROLE app SET search_path TO myapp;
DROP ROLE app;
```

### Privilegios

```
GRANT ALL ON DATABASE mydb TO app;
GRANT SELECT, INSERT ON users TO reader;
GRANT USAGE ON SCHEMA public TO app;
REVOKE INSERT ON users FROM reader;
```

### Seguridad a Nivel de Fila

```
ALTER TABLE users ENABLE ROW LEVEL SECURITY;
CREATE POLICY user_own ON users
FOR ALL USING (id = current_setting('app.uid')::INT);
```

## Soporte JSON

### Operadores JSONB

| Command | Description |
|---------|-------------|
| `->'key'` | Obtener valor JSON por clave (como JSON) |
| `->>'key'` | Obtener valor JSON por clave (como texto) |
| `#>'{a,b}'` | Obtener valor anidado por ruta |
| `@>` | Contiene (izquierda incluye derecha) |
| `?` | La clave existe |
| `\|\|` | Concatenar valores JSONB |

### Consultas JSONB

```
SELECT data->>'name' FROM profiles
WHERE data @> '{"active": true}';

SELECT * FROM profiles
WHERE data ? 'email';
```

### Funciones JSONB

```
SELECT jsonb_each(data) FROM profiles;
SELECT jsonb_array_elements('[1,2,3]');
SELECT jsonb_set(data, '{name}', '"Alice"')
FROM profiles WHERE id = 1;
```

## Patrones Comunes

### Transacciones

```
BEGIN;
UPDATE accounts SET balance = balance - 100
WHERE id = 1;
UPDATE accounts SET balance = balance + 100
WHERE id = 2;
COMMIT;  -- or ROLLBACK;
```

### Funciones de Ventana

```
SELECT name, salary,
  RANK() OVER (ORDER BY salary DESC),
  AVG(salary) OVER (PARTITION BY dept)
FROM employees;
```

### Copiar Datos

```
COPY users TO '/tmp/users.csv'
WITH (FORMAT csv, HEADER);
COPY users FROM '/tmp/users.csv'
WITH (FORMAT csv, HEADER);
```

### Respaldo con pg_dump

```
pg_dump -U postgres mydb > backup.sql
pg_dump -Fc mydb > backup.dump
pg_restore -d mydb backup.dump
```