如何在sql中根据第一个月的采购组保留价值并计算下一次采购金额

我想创建客户保留

所以我有一张桌子：

身份证件 日期 购买 1. 2020-01 200 2. 2020-12 100 2. 2020-03 150 3. 2020-03 200 1. 2020-07 120 1. 2020-08 300 3. 2020-05 250

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您可以使用窗口函数和通用表表达式轻松完成此操作

架构和插入语句：

 create table purchases(id int, date date, purchase int);
 insert into purchases values(1,    '2020-01',  200);
 insert into purchases values(2,    '2020-12',  100);
 insert into purchases values(2,    '2020-03',  150);
 insert into purchases values(3,    '2020-03',  200);
 insert into purchases values(1,    '2020-07',  120);
 insert into purchases values(1,    '2020-08',  300);
 insert into purchases values(3,    '2020-05',  250);     

查询：

with cte as
     ( 
       select id,date,purchase,
       min(date)over(partition by id) FirstPurchaseMonth from purchases
     )
     ,cte2 as
     (
       select substr(date,6,2)-substr(firstpurchasemonth,6,2) Purchasemonth, max(FirstPurchaseMonth)firstpurchasemonth, 
       purchase,sum(purchase)total from cte
       group by firstpurchasemonth,substr(date,6,2)-substr(firstpurchasemonth,6,2) 
     )
     select purchasemonth,firstpurchasemonth,sum(total)over(partition by firstpurchasemonth order by purchasemonth)total
     from cte2 
 

输出：

采购月 第一个月 全部的 0 2020-01 200 6. 2020-01 320 7. 2020-01 620 0 2020-03 350 2. 2020-03 600 9 2020-03 700

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请记住，选择标记时，

jQuery

和

Query

是不同的