sql - 从多个日期范围中提取每周天数

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

我想计算与给定周重叠的旅行天数。表中的行程具有包含边界。每周从星期一开始，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

日历引用:

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编写此代码，但我更喜欢在 Postgres 中执行此操作，但我不清楚从哪里开始...

Answer 1

您似乎需要generate_series() 以及join 和group by。计算涵盖的周数:

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:

我知道你想要涵盖的日子。这是聚合中稍微多一点的工作:

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:这不会返回您所拥有的准确结果。我认为这些是正确的。