I have this table:

CREATE TABLE runner_orders (
  "order_id" integer,
  "runner_id" integer,
  "distance" decimal (5,2),
  "duration" decimal (5,2),
  "cancellation" varchar(23)
);

INSERT INTO runner_orders
  ("order_id", "runner_id", "distance", "duration", "cancellation")
VALUES
  (1, 1,  20, 32, ''),
  ('2', '1',  20, 27, ''),
  ('3', '1',  13.4, 20, ''),
  ('4', '2',  23.4, 40, ''),
  ('5', '3',  10, 15, ''),
  ('6', '3',  NULL, NULL, 'Restaurant Cancellation'),
  ('7', '2',  25, 25, ''),
  ('8', '2',  23.4, 15, ''),
  ('9', '2',  NULL, NULL, 'Customer Cancellation'),
  ('10', '1', 10, 10, '');

And they ask me:

What is the successful delivery percentage for each runner?

I did this, that finally gave me the correct results:

WITH cte_1
AS (
  SELECT runner_id, (COUNT(runner_id))*100 AS percentages
  FROM runner_orders 
  WHERE cancellation = ''
  group by runner_id
)
SELECT cte_1.runner_id, (percentages/(COUNT(ru.cancellation))) as percentages_successful_deliveries
FROM cte_1
FULL JOIN runner_orders AS ru
  ON cte_1.runner_id = ru.runner_id
GROUP BY cte_1.runner_id, cte_1.percentages
ORDER BY runner_id

But I wonder, How can I get the same results in a shorter query? I tried subqueries, and It didn't work for me. This is one of the many subqueries I tried:

SELECT runner_id, ((COUNT(runner_id) over (PARTITION BY runner_id, cancellation))*100)/(count(runner_id))
FROM runner_orders
group by runner_id, cancellation

So how I can make this work in a shorter and more simple way than a CTE.