Collect rating statistics using postgresql - postgresql

Question

I am currently trying to collect rating statistics from a postgreSql database. Below you can find a simplified example of the database schema I would like to query.
CREATE DATABASE test_db;
CREATE TABLE rateable_object (
id BIGSERIAL PRIMARY KEY,
cdate TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
mdate TIMESTAMP,
name VARCHAR(160) NOT NULL,
description VARCHAR NOT NULL
);
CREATE TABLE ratings (
id BIGSERIAL PRIMARY KEY,
cdate TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
mdate TIMESTAMP,
parent_id BIGINT NOT NULL,
rating INTEGER NOT NULL DEFAULT -1
);
I would now like to collect a statistic for the values in the ratings column. The response should look like this:
+--------------+-------+
| column_value | count |
+--------------+-------+
| -1 | 2 |
| 0 | 45 |
| 1 | 37 |
| 2 | 13 |
| 3 | 5 |
| 4 | 35 |
| 5 | 75 |
+--------------+-------+
My first solution (see below) is very naive and probably not the fastest and simplest one. So my question is, if there is a better solution.
WITH
stars AS (SELECT generate_series(-1, 5) AS value),
votes AS (SELECT * FROM ratings WHERE parent_id = 1)
SELECT
stars.value AS stars, coalesce(COUNT(votes.*), 0) as votes
FROM
stars
LEFT JOIN
votes
ON
votes.rating = stars.value
GROUP BY stars.value
ORDER BY stars.value;
As I would not like to waste your time, I prepared some test data for you:
INSERT INTO rateable_object (name, description) VALUES
('Penguin', 'This is the Linux penguin.'),
('Gnu', 'This is the GNU gnu.'),
('Elephant', 'This is the PHP elephant.'),
('Elephant', 'This is the postgres elephant.'),
('Duck', 'This is the duckduckgo duck.'),
('Cat', 'This is the GitHub cat.'),
('Bird', 'This is the Twitter bird.'),
('Lion', 'This is the Leo lion.');
CREATE OR REPLACE FUNCTION generate_test_data() RETURNS INTEGER LANGUAGE plpgsql AS
$$
BEGIN
FOR i IN 0..1000 LOOP
INSERT INTO ratings (parent_id, rating) VALUES
(
(1 + (10 - 1) * random())::numeric::int,
(-1 + (5 + 1) * random())::numeric::int
);
END LOOP;
RETURN 0;
END;
$$;
SELECT generate_test_data();