Getting around the constraint "column must appear in the GROUP BY clause or be used in an aggregate function" I'm using Postgres, which enforces the constraint that all columns in a SELECT...GROUP BY must appear in the GROUP BY clause or be used in an aggregate function.

Lets say I'm modelling peoples' cars, and I want to work out a person's name, license number, and how many cars they have. Here's my example as an SQL Fiddle.

I would have the following schema:

CREATE TABLE person(
  id integer PRIMARY KEY,
  name text
);

CREATE TABLE license(
  person_id integer REFERENCES person(id),
  expiry_date date
);

CREATE TABLE car(
  owner_id integer REFERENCES person(id),
  registration_number TEXT
);


Here's the query:

SELECT person.name, person.id, license.expiry_date, COUNT(car) FROM person
  JOIN license ON license.person_id = person.id
  JOIN car ON car.owner_id = person.id
WHERE person.name = 'Charles Bannerman'
GROUP BY person.id;


I know, because of my own business logic, that one person can only have one license, so when I join to the person, even though it's GROUP BY'd, I should be able to find their license number. However because it isn't part of the GROUP BY statement and doesn't use an aggregate function, I can't access it. 

How should I write this query in an idiomatic way. I've seen vague things about LATERAL JOINs, window functions, and subqueries, but I'm not sure the best way to answer this question.
seharusnya seperti ini(supposed to be like this): 

SELECT person.name, person.id, license.expiry_date, COUNT(car) FROM person
  JOIN license ON license.person_id = person.id
  JOIN car ON car.owner_id = person.id
WHERE person.name = 'Charles Bannerman'
GROUP BY person.name, person.id, license.expiry_date, car.car;