从定价表中获取每个季度的第一个价格

如何解决从定价表中获取每个季度的第一个价格

我有一个包含以下字段的定价表：

id
start_date
price

我想获取每个季度的首个价格，我该如何实现？

我试过了：

SELECT id,price,EXTRACT(YEAR FROM start_date::TIMESTAMP) AS year,EXTRACT(QUARTER FROM start_date::TIMESTAMP) AS quarter,min(start_date) as start_date
FROM pricing
GROUP BY id,EXTRACT(YEAR FROM start_date::TIMESTAMP),EXTRACT(QUARTER FROM start_date::TIMESTAMP)

但如果价格发生变化，我将获得所有季度价格，我只需要每个季度的第一个价格。

谢谢！

解决方法

可能有数百种方法来实现它。您可以首先在 CTE 或子查询中创建您需要的季度，以便您可以将其与您的定价表进行比较，例如

样本数据

CREATE TEMPORARY TABLE pricing (id INT,start_date DATE,price NUMERIC);
INSERT INTO pricing VALUES 
  (5,CURRENT_DATE,1.99),(4,CURRENT_DATE-2,0.99),(3,CURRENT_DATE-3,0.42),(2,CURRENT_DATE-100,0.10),(1,CURRENT_DATE-121,0.82);

查询

WITH q (year,quarter) AS (
  SELECT DISTINCT
    EXTRACT(YEAR FROM start_date::TIMESTAMP),EXTRACT(QUARTER FROM start_date::TIMESTAMP) 
  FROM pricing
)
SELECT *,(SELECT price 
           FROM pricing 
           WHERE EXTRACT(QUARTER FROM start_date::TIMESTAMP) = q.quarter AND
                 EXTRACT(YEAR FROM start_date::TIMESTAMP) = q.year
           ORDER BY start_date LIMIT 1) 
FROM q ORDER BY q.year,q.quarter;

 year | quarter | price 
------+---------+-------
 2020 |       4 |  0.82
 2021 |       1 |  0.42

演示：db<>fiddle

EDIT：根据您的用例，您可能希望使用类似 generate_series 的东西生成年份和季度，而不是在 pricing 上运行完整扫描，如示例所示上面，例如

SELECT 
  EXTRACT(YEAR FROM d) AS year,EXTRACT(QUARTER FROM d) AS quarter
FROM generate_series('2019-01-01'::DATE,'3 month') AS d
ORDER BY 1,2;

 year | quarter 
------+---------
 2019 |       1
 2019 |       2
 2019 |       3
 2019 |       4
 2020 |       1
 2020 |       2
 2020 |       3
 2020 |       4
 2021 |       1