SQL 嵌套逻辑

Question

这是我的table结构

CUST_ID  ORDER_DT
1        01-2013
1        04-2013
1        01-2015
1        02-2015

我想要实现的是将客户分类为新 customer/existing 客户并恢复。逻辑是第一次订货-新从上次购买到现有的 365 天内的时间时间超过 1 年然后复活

我的输出应该是

CUST_ID  ORDER_DT  FLAG
1         01-2013  New
1         04-2013  Exisiting
1         01-2015  Revived
1         02-2015  Exisiting

我的SQL

select a.cust_id,a.order_dt,coalesce(b.ptye,'other') as typ
from tab a left join
  (select min(order_dt),new as ptye from tab group by cust_id) b on a.cust_id=b.cust_id

如何用嵌套逻辑替换另一个。

Answer 1

一个非常简单的方法是使用带子查询的 case 语句：

select cust_id
, order_dt
, flag = case
             when (select COUNT(*) from myTable x where t.cust_id= x.cust_id and x.order_dt < t.order_dt and DATEDIFF(DD, x.order_dt , t.order_dt ) < 365) then 'Existing'
             when (select COUNT(*) from myTable x where t.cust_id= x.cust_id and x.order_dt < t.order_dt and DATEDIFF(DD, x.order_dt , t.order_dt ) >= 365) then 'Revived'
             else 'New'
         end
from myTable t

Answer 2

最好的方法是使用 lag()。 Teradata 不太支持延迟，但它确实支持其他 window 功能。所以，你可以模仿一下：

select t.cust_id, t.order_dt,
       (case when order_dt - prev_od <= 365 then 'Existing' else 'New'
        end) as flag
from (select t.*,
             max(order_dt) over (partition by cust_id order by order_dt
                                 rows between 1 preceding and 1 preceding
                                ) as prevod
      from mytable t
     ) t;

我应该指出您实际上不需要子查询，但我认为它有助于提高可读性：

select t.cust_id, t.order_dt,
       (case when order_dt -
                  max(order_dt) over (partition by cust_id order by order_dt
                                 rows between 1 preceding and 1 preceding
                                ) <= 365
             then 'Existing' else 'New'
        end) as flag
from (select t.*,
              as prevod
      from mytable t
     ) t;

Answer 3

这包括 Gordon 的回答中缺少的 "revived" 逻辑：

SELECT 
   CUST_ID, ORDER_DT,
   CASE
      WHEN ORDER_DT = MIN(ORDER_DT)  -- first order 
                      OVER (PARTITION BY CUST_ID)
         THEN 'New'
      WHEN ORDER_DT >= MAX(ORDER_DT)  -- more than 365 days since previous order
                       OVER (PARTITION BY CUST_ID
                             ORDER BY ORDER_DT
                             ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) + 365
         THEN 'Revived'
      ELSE 'Existing'
   END
FROM tab

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