根据每个国家/地区的预定义份额将固定价值拆分到国家/地区

Question

DB-Fiddle

CREATE TABLE costs (
    id SERIAL PRIMARY KEY,
    event_date DATE,
    country VARCHAR,
    channel VARCHAR,
    costs DECIMAL
);

INSERT INTO costs
(event_date, country, channel, costs)
VALUES 
('2020-02-08', 'DE', 'channel_01', '400'),
('2020-02-08', 'DE', 'channel_02', '400'),
('2020-02-08', 'DE', 'channel_03', '400'),
('2020-02-08', 'FR', 'channel_01', '400'),
('2020-02-08', 'FR', 'channel_02', '400'),
('2020-02-08', 'NL', 'channel_01', '400'),

('2020-04-15', 'DE', 'channel_01', '300'),
('2020-04-15', 'FR', 'channel_01', '300'),
('2020-04-15', 'NL', 'channel_01', '300'),
('2020-04-15', 'NL', 'channel_02', '300'),
('2020-04-15', 'NL', 'channel_03', '300');

预期结果：

event_date    |    country   |            costs            |
--------------|--------------|-----------------------------|---------
2020-02-08    |      DE      |        240  (=400 x 0.6)    |    
2020-02-08    |      FR      |        120  (=400 x 0.3)    |   
2020-02-08    |      NL      |         40  (=400 x 0.1)    |   
--------------|--------------|-----------------------------|---------
2020-04-15    |      DE      |        180  (=300 x 0.6)    |   
2020-04-15    |      FR      |         90  (=300 x 0.3)    |   
2020-04-15    |      NL      |         30  (=300 x 0.1)    |   

---

我想根据预定义的份额将costs拆分为每天每个国家/地区。
股份是：DE = 0.6, FR = 0.3, NL = 0.1

SELECT
c.event_date,
c.country,
c.costs
FROM costs c
GROUP BY 1,2,3
ORDER BY 1,2;

你知道我需要什么查询来实现这个吗？

Answer 1

只需使用CASE 表达式：

SELECT c.event_date,
       c.country,
       (CASE WHEN c.country = 'DE' THEN 0.6 * c.costs
             WHEN c.country = 'FR' THEN 0.3 * c.costs
             WHEN c.country = 'NL' THEN 0.1 * c.costs
        END) as allocated_costs
FROM costs c
GROUP BY c.event_date, c.country, c.costs
ORDER BY 1, 2;

如果您愿意，可以更方便地将值存储在派生表中：

SELECT c.event_date, c.country, (v.alloc * c.costs) as allocated_costs
FROM costs c JOIN
     (VALUES ('DE', 0.6), ('FR', 0.3), ('NL', 0.1)
     ) v(country, alloc)
     USING (country)
GROUP BY c.event_date, c.country, c.costs, v.alloc
ORDER BY 1, 2;

Here 是一个 dbfiddle。

Answer 2

最好的方法是将这些费率添加到表中并在查询中使用该表。

说明如何在查询中使用硬编码值：

SELECT
c.event_date,
c.country,
c.costs * case country when  'DE' then 0.6 
          when 'FR' then 0.3
          when 'NL' then 0.1 
          end 
FROM costs c
GROUP BY 1,2,3
ORDER BY 1,2;