Funciones de agregado

-- Funciones de agregado: Calcular totales, medias,...

-- Contando el número de actores de la tabla actor (COUNT)
select count(*) total from actor;

-- Sumar valores (SUM)
select sum(amount) total from payment;

-- Obtener una media (AVG)
select avg(amount) media from payment;

-- Obtener máximo y mínimo (MIN,MAX)
select min(amount) minimo, max(amount) maximo from payment;

https://www.w3schools.com/sql/sql_aggregate_functions.asp