Sql 在列上进行区分，并在postgres中查找过去几个月的总和

我有一个类似于此示例的表格：

     purchase_datetime    customer_id  value    purchase_id
    2013-01-08 17:13:29      45236       92        2526
    2013-01-03 15:42:35      45236       16        2565
    2013-01-03 15:42:35      45236       16        2565
    2013-03-08 09:04:52      45236       636       2563
    2013-12-08 12:12:24      45236       23        2505
    2013-12-08 12:12:24      45236       23        2505
    2013-12-08 12:12:24      45236       23        2505
    2013-12-08 12:12:24      45236       23        2505
    2013-07-08 22:35:53      35536       73        2576
    2013-07-08 09:52:03      35536        4        5526
    2013-10-08 16:23:29      52626       20        2226
...
    2013-04-08 17:49:31      52626       27        4526
    2013-12-09 20:40:53      52626       27        4626

现在，我需要找到客户在过去几个月内每次购买（购买id）的总花费金额（价值）。但是我有一个问题，因为有两倍的购买id，所以我需要在购买id上进行区分

这就是我到目前为止在没有distinct的情况下得到的，我不知道如何接近distinct

Select customer_id
  sum(case when ( date '2017-01-01'  - purchase_datetime::DATE <=30) then value else 0 end)  as 1month,
  sum( case when ( date '2017-01-01' - purchase_datetime::DATE <=90) then value else 0 end)  as 3month,
  sum( case when ( date '2017-01-01' - purchase_datetime::DATE <=180) then value else 0 end)  as 6month,
  sum( case when ( date '2017-01-01' - purchase_datetime::DATE <=360) then value else 0 end)  as 12month

FROM table_data
GROUP BY (customer_id)
ORDER BY amount_1month DESC;

---

您可以在子查询上选择，并在该子查询中使用DISTINCT（或GROUP BY）

例如：

---

测试数据：

create table table_data (purchase_datetime timestamp(0),customer_id int,"value" int,purchase_id int);
insert into table_data (purchase_datetime,customer_id,"value",purchase_id) values
(current_timestamp - interval '11 month',45236,92,2526),
(current_timestamp - interval '11 month',45236,16,2565),
(current_timestamp - interval '1 month',45236,16,2565),
(current_timestamp - interval '2 month',45236,636,2563),
(current_timestamp - interval '5 month',45236,23,2505),
(current_timestamp - interval '5 month',45236,23,2505),
(current_timestamp - interval '5 month',45236,23,2505),
(current_timestamp - interval '3 month',35536,73,2576),
(current_timestamp - interval '2 month',35536,4,5526),
(current_timestamp - interval '1 month',52626,20,2226),
(current_timestamp - interval '6 month',52626,27,4526),
(current_timestamp - interval '6 month',52626,27,4626);

---

我不明白你为什么要来这里？您的分组依据将不会返回任何重复的行。@jarlh如果我删除分组依据怎么办？我不确定，但当我这样做时，我得到了一个巨大的数字，因为有多行数据相同，就像第五行到第九行一样。使用GROUP BY，每个客户id可以得到一行。这不是你想要的吗？@jarlh我想要一行购买id，例如，我从第五行到第八行有4行数据相同，我需要3行数据才能消失，从数据中删除。所需的输出不显示总和。它仅仅是

从表数据中选择distinct*

。这就是你想要的吗？

SELECT 
  customer_id, 
  sum(case when purchase_datetime::DATE between current_date - interval '1 month' and current_date then "value" else 0 end)  as "1month",
  sum(case when purchase_datetime::DATE between current_date - interval '3 month' and current_date then "value" else 0 end)  as "3month",
  sum(case when purchase_datetime::DATE between current_date - interval '6 month' and current_date then "value" else 0 end)  as "6month",
  sum(case when purchase_datetime::DATE between current_date - interval '1 year' and current_date then "value" else 0 end)  as "12month"
FROM (
  select 
  distinct purchase_id, customer_id, purchase_datetime,  "value"

  -- distinct on (purchase_id) customer_id, purchase_datetime, "value" 
  -- Note: with this type of distinct you assume that for each purchase_id there is only 1 combination of the 3 other field values.

  from table_data
) p
GROUP BY customer_id
ORDER BY "1month" DESC;

create table table_data (purchase_datetime timestamp(0),customer_id int,"value" int,purchase_id int);
insert into table_data (purchase_datetime,customer_id,"value",purchase_id) values
(current_timestamp - interval '11 month',45236,92,2526),
(current_timestamp - interval '11 month',45236,16,2565),
(current_timestamp - interval '1 month',45236,16,2565),
(current_timestamp - interval '2 month',45236,636,2563),
(current_timestamp - interval '5 month',45236,23,2505),
(current_timestamp - interval '5 month',45236,23,2505),
(current_timestamp - interval '5 month',45236,23,2505),
(current_timestamp - interval '3 month',35536,73,2576),
(current_timestamp - interval '2 month',35536,4,5526),
(current_timestamp - interval '1 month',52626,20,2226),
(current_timestamp - interval '6 month',52626,27,4526),
(current_timestamp - interval '6 month',52626,27,4626);

select customer_id, sum(value)
from (
    select distinct on (purchase_id) *
    from t
) s
where purchase_datetime >= '2017-07-01'
group by 1
;
 customer_id | sum 
-------------+-----
       35536 |  77
       52626 |  20
       45236 |  23