Question

我在PostgreSQL 10.5中有一个表trips：

id  start_date    end_date
----------------------------
1   02/01/2019    02/03/2019
2   02/02/2019    02/03/2019
3   02/06/2019    02/07/2019
4   02/06/2019    02/14/2019
5   02/06/2019    02/06/2019

我想计算出与给定星期重叠的旅行天数。表中的行程具有包含范围。几周从星期一开始，到星期日结束。预期结果将是：

week_of    days_utilized
------------------------
01/28/19    5
02/04/19    8
02/11/19    4

有关日历的参考：

Monday 01/28/19 - Sunday 02/03/19
Monday 02/04/19 - Sunday 02/10/19
Monday 02/11/19 - Sunday 02/17/19

我知道如何用我使用的编程语言来编写代码，但是我更喜欢在Postgres中编写代码，而且不清楚从哪里开始...

Answer 1

您似乎想要generate_series()以及join和group by。要计算所涵盖的一周：

select gs.wk, count(t.id) as num_trips
from generate_series('2019-01-28'::date, '2019-02-11'::date, interval '1 week') gs(wk) left join
     trips t
     on gs.wk <= t.end_date and
        gs.wk + interval '6 day' >= t.start_date
group by gs.wk
order by gs.wk;

编辑：

我看到你希望日子过得好。聚合中需要做的工作更多：

select gs.wk, count(t.id) as num_trips,
       sum( 1 +
            extract(day from (least(gs.wk + interval '6 day', t.end_date) - greatest(gs.wk, t.start_date)))
          ) as days_utilized
from generate_series('2019-01-28'::date, '2019-02-11'::date, interval '1 week') gs(wk) left join
     trips t
     on gs.wk <= t.end_date and
        gs.wk + interval '6 day' >= t.start_date
group by gs.wk
order by gs.wk;

注意：这不会完全返回您得到的结果。我认为这些是正确的。

Answer 2

为此，我会考虑range types。使用range operators使计算更简单明了-我在下面使用了重叠&&和交集*。如果表很大，我们可以使用功能性GiST or SP-GiST index来快速进行查询。喜欢：

CREATE INDEX trip_range_idx ON trip
USING gist (daterange(start_date, end_date, '[]'));

然后您的查询可以使用此索引：

SELECT week
     , count(overlap)                       AS ct_trips
     , sum(upper(overlap) - lower(overlap)) AS days_utilized
FROM  (
   SELECT week, trip * week AS overlap
   FROM  (
      SELECT daterange(mon::date, mon::date + 7) AS week
      FROM   generate_series(timestamp '2019-01-28'
                           , timestamp '2019-02-11'
                           , interval  '1 week') mon
      ) w
   LEFT   JOIN (SELECT daterange(start_date, end_date, '[]') FROM trip) t(trip) ON trip && week
   ) sub
GROUP  BY 1
ORDER  BY 1;

db <>提琴here

请注意，默认情况下，date_range由包含的下限和包含 exclusive 的上限组成。您的范围的上限和下限 include ，因此请使用以下内容创建daterange：daterange(start_date, end_date, '[]')。函数upper()仍返回互斥上限。因此，表达式upper(overlap) - lower(overlap)可以正确地计算天数。

我将generate_series()与timestamp输入一起使用是有原因的：

Generating time series between two dates in PostgreSQL

从多个日期范围中提取每周的天数

2 个答案: