使用从某个月份开始的 12 个月周期迭代日期

如何解决使用从某个月份开始的 12 个月周期迭代日期

DB-Fiddle

CREATE TABLE customers (
    id SERIAL PRIMARY KEY,order_date DATE,customer VARCHAR(255)
);

INSERT INTO customers
(order_date,customer)
VALUES 
('2020-05-10','user_01'),('2020-05-15',('2020-05-18','user_02'),('2020-05-26','user_03'),('2020-06-03','user_04'),('2020-06-05','user_05'),('2020-06-24','user_06'),('2021-05-02',('2021-05-05',('2021-05-12',('2021-05-20','user_07'),('2021-06-08',('2021-06-20',('2021-06-21','user_08'),('2021-06-25','user_09');

预期结果：

order_date   |   customer  |  
-------------|-------------|----
2021-05-02   |   user_01   |  
2021-05-05   |   user_01   |  
2021-05-12   |   user_03   |  
-------------|-------------|----
2021-06-08   |   user_04   |  
2021-06-20   |   user_06   |  

---

我想列出某个月份的所有客户

a) 在过去 12 个月没有存在并且
b) 在 12 个月之前已经存在。

---

对于一个月，我可以通过使用此查询来实现这一点：

SELECT
c1.order_date,c1.customer
FROM customers c1
WHERE c1.order_date BETWEEN '2021-05-01 00:00:00' AND '2021-05-31 23:59:59'

/* Check if customer exists in the past 12 months */
AND NOT EXISTS

   (SELECT
    c2.customer
    FROM customers c2
    WHERE c2.order_date BETWEEN '2020-06-01 00:00:00' AND '2021-04-30 23:59:59'
    AND c2.customer = c1.customer)

/* Check if customer exists before the past 12 months */
AND EXISTS

   (SELECT
    c2.customer
    FROM customers c2
    WHERE c2.order_date < '2020-06-01 00:00:00'
    AND c2.customer = c1.customer)

ORDER BY 2;

---

但是，我必须每月单独运行此查询。

因此，我想知道是否有一个迭代解决方案可以一次经历几个月。

在上面的例子中，它会运行 BETWEEN '2021-05-01 00:00:00' AND '2021-06-30 23:59:59' 并计算从 5 月开始的 12 个月，在下一步中从 6 月开始 12 个月，以获得预期结果。

你知道这是否可行吗？

解决方法

SELECT 
t1.order_date,t1.customer
FROM 

  (SELECT
   c.customer,c.order_date,LAG(c.order_date) OVER (PARTITION BY c.customer ORDER BY c.order_date) AS prev_order_date
   FROM customers c) t1

WHERE t1.order_date BETWEEN '2021-05-01' AND '2021-06-30' 
AND t1.prev_order_date >= date_trunc('month',t1.order_date) - interval '12 month'
AND t1.prev_order_date < date_trunc('month',t1.order_date)
ORDER BY 1,2;

DB-Fiddle