【发布时间】：2016-11-19 15:23:55
【问题描述】：
使用 Postgres 9.5。测试数据：
create temp table rental (
customer_id smallint
,rental_date timestamp without time zone
,customer_name text
);
insert into rental values
(1, '2006-05-01', 'james'),
(1, '2006-06-01', 'james'),
(1, '2006-07-01', 'james'),
(1, '2006-07-02', 'james'),
(2, '2006-05-02', 'jacinta'),
(2, '2006-05-03', 'jacinta'),
(3, '2006-05-04', 'juliet'),
(3, '2006-07-01', 'juliet'),
(4, '2006-05-03', 'julia'),
(4, '2006-06-01', 'julia'),
(5, '2006-05-05', 'john'),
(5, '2006-06-01', 'john'),
(5, '2006-07-01', 'john'),
(6, '2006-07-01', 'jacob'),
(7, '2006-07-02', 'jasmine'),
(7, '2006-07-04', 'jasmine');
我正在尝试了解现有客户的行为。我试图回答这个问题：
根据上一次下单的时间（当月、上月 (m-1)...到 m-12），客户再次下单的可能性有多大？
可能性计算如下：
distinct count of people who ordered in current month /
distinct count of people in their cohort.
因此，我需要生成一个表格，列出当月订购的人数，这些人数属于给定群组。
那么，加入队列的规则是什么？
- current month cohort: >1 order in month OR (1 order in month given no previous orders)
- m-1 cohort: <=1 order in current month and >=1 order in m-1
- m-2 cohort: <=1 order in current month and 0 orders in m-1 and >=1 order in m-2
- etc
我使用 DVD Store 数据库作为示例数据来开发查询：http://linux.dell.com/dvdstore/
以下是同类群组规则和聚合的示例，基于 7 月是
"month's orders being analysed"（请注意："month's orders being analysed" 列是下面“所需输出”表中的第一列）：
customer_id | jul-16| jun-16| may-16|
------------|-------|-------|-------|
james | 1 1 | 1 | 1 | <- member of jul cohort, made order in jul
jasmine | 1 1 | | | <- member of jul cohort, made order in jul
jacob | 1 | | | <- member of jul cohort, did NOT make order in jul
john | 1 | 1 | 1 | <- member of jun cohort, made order in jul
julia | | 1 | 1 | <- member of jun cohort, did NOT make order in jul
juliet | 1 | | 1 | <- member of may cohort, made order in jul
jacinta | | | 1 1 | <- member of may cohort, did NOT make order in jul
此数据将输出下表：
--where m = month's orders being analysed
month's orders |how many people |how many people from |how many people |how many people from |how many people |how many people from |
being analysed |are in cohort m |cohort m ordered in m |are in cohort m-1 |cohort m-1 ordered in m |are in cohort m-2 |cohort m-2 ordered in m |...m-12
---------------|----------------|----------------------|------------------|------------------------|------------------|------------------------|
may-16 |5 |1 | | | | |
jun-16 | | |5 |3 | | |
jul-16 |3 |2 |2 |1 |2 |1 |
到目前为止，我的尝试是在以下方面的变化：
generate_series()
和
row_number() over (partition by customer_id order by rental_id desc)
我还没能把所有东西都放在一起（我已经尝试了好几个小时，但还没有解决）。
为了可读性，我认为将我的工作分部分发布更好（如果有人希望我完整发布 sql 查询，请发表评论 - 我会添加它）。
系列查询：
(select
generate_series(date_trunc(‘month’,min(rental_date)),date_trunc(‘month’,max(rental_date)),’1 month)) as month_being_analysed
from
rental) as series
排名查询：
(select
*,
row_number() over (partition by customer_id order by rental_id desc) as rnk
from
rental
where
date_trunc('month',rental_date) <= series.month_being_analysed) as orders_ranked
我想做一些类似的事情：对系列查询返回的每一行运行 orders_ranked 查询，然后根据 orders_ranked 的每次返回进行聚合。
类似：
(--this query counts the customers in cohort m-1
select
count(distinct customer_id)
from
(--this query ranks the orders that have occured <= to the date in the row of the 'series' table
select
*,
row_number() over (partition by customer_id order by rental_id desc) as rnk
from
rental
where
date_trunc('month',rental_date)<=series.month_being_analysed) as orders_ranked
where
(rnk=1 between series.month_being_analysed - interval ‘2 months’ and series.month_being_analysed - interval ‘1 months’)
OR
(rnk=2 between series.month_being_analysed - interval ‘2 months’ and series.month_being_analysed - interval ‘1 months’)
) as people_2nd_last_booking_in_m_1,
(--this query counts the customers in cohort m-1 who ordered in month m
select
count(distinct customer_id)
from
(--this query returns the orders by customers in cohort m-1
select
count(distinct customer_id)
from
(--this query ranks the orders that have occured <= to the date in the row of the 'series' table
select
*,
row_number() over (partition by customer_id order by rental_id desc) as rnk
from
rental
where
date_trunc('month',rental_date)<=series.month_being_analysed) as orders_ranked
where
(rnk=1 between series.month_being_analysed - interval ‘2 months’ and series.month_being_analysed - interval ‘1 months’)
OR
(rnk=2 between series.month_being_analysed - interval ‘2 months’ and series.month_being_analysed - interval ‘1 months’)
where
rnk=1 in series.month_being_analysed
) as people_who_booked_in_m_whose_2nd_last_booking_was_in_m_1,
...
from
(select
generate_series(date_trunc(‘month’,min(rental_date)),date_trunc(‘month’,max(rental_date)),’1 month)) as month_being_analysed
from
rental) as series
【问题讨论】：
-
请提供准确的表定义以及相关列
rental_id、customer_id、rental_date的数据类型和所有约束。理想情况下是有效的CREATE TABLEstatement。 （我不会自己从链接的存档中提取它。）而且，总是，你的 Postgres 版本。 -
还有：
current month cohort: >1 order in month。我怀疑在您定义的所有实例中都应该是>=？请说清楚。还有：基数？每个客户和每月有多少订单：最小、最大、平均？ -
@ErwinBrandstetter 我已经添加了测试数据（dvdrental db 的 .tar 文件和相关命令） - 我试图只转储表格，但遇到了问题 - 希望是我已经添加了足够的。你是对的，队列应该是
>=，我添加了一个表格，显示了队列规则的作用——希望这可以澄清事情。我已将 Postgres 版本添加到顶部 - 9.5。就数据量而言 - 数百万行。每月客户：数十万，每月平均订单 -
另外，你在 codementor 吗？ :-)
-
将测试数据从 .tar 文件更改为插入命令。
标签： sql postgresql crosstab window-functions generate-series