Why does aggregate query allow select of non-group by or aggregate values?

[Jack Christensen <jackc@xxxxxxxxxxxxxxxxx>]

CREATE TABLE people(
  id serial PRIMARY KEY,
  name varchar NOT NULL
);

INSERT INTO people(name) VALUES('Adam'), ('Adam'), ('Adam'), ('Bill'), 
('Sam'), ('Joe'), ('Joe');

SELECT name, count(*), random()
FROM people
GROUP BY name;


I would expect this query to cause an error because of random(). I ran 
into this using an array produced by a subquery as a column in the 
select of an aggregate query, but I was able to boil it down to this 
contrived example. Shouldn't any expression that is not in the group by 
or an aggregate function be rejected?

What am I not understanding?

Thanks.

--
Jack Christensen
jackc@xxxxxxxxxxxxxxxxx


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