获取组的百分比

Question

我有这个数据：

CREATE TABLE tickets(user_id int NOT NULL);
INSERT INTO tickets VALUES (1);
INSERT INTO tickets VALUES (2);
INSERT INTO tickets VALUES (3); -- 3 times
INSERT INTO tickets VALUES (4); -- 10 times

现在我想显示每个用户的票数百分比。

我试过这个：

WITH number_of_tickets AS (
  SELECT user_id, COUNT(user_id) AS number_of_tickets_per_user
  FROM tickets 
  GROUP BY user_id
)
SELECT 
  number_of_tickets_per_user, 
  ROUND((COUNT(user_id) * 100.0) / (SELECT COUNT(DISTINCT(user_id)) FROM tickets), 3) -- No no no no
FROM number_of_tickets
GROUP BY number_of_tickets_per_user
ORDER BY number_of_tickets_per_user;

但我可能不能很好地处理百分比计算。结果总是显示每个用户每个票数的 25%。

谢谢

Answer 1

我建议使用窗口函数：

 SELECT DISTINCT user_id,
        (count(*) over (partition by user_id) / count(*) over ()::numeric)
   FROM tickets
   ORDER BY user_id;

 user_id |        ?column?
---------+------------------------
       1 | 0.06666666666666666667
       2 | 0.06666666666666666667
       3 | 0.20000000000000000000
       4 | 0.66666666666666666667
(4 rows)

Answer 2

WITH number_of_tickets AS (
  SELECT user_id, COUNT(user_id) AS number_of_tickets_per_user
  FROM tickets 
  GROUP BY user_id
),
total_tickets AS (
  SELECT SUM(number_of_tickets_per_user) total_tickets
  FROM number_of_tickets
)
SELECT 
  user_id,
  number_of_tickets_per_user, 
  ROUND(number_of_tickets_per_user / total_tickets,3) percent
FROM number_of_tickets, total_tickets;