从多个日期范围中提取每周的天数

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

我想计算与给定周数重叠的旅行天数。表中的旅行具有包容性界限。周从周一开始，周日结束。预期结果将是：

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

对于日历参考：

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写这个，但我更喜欢在Postgres中这样做，我不清楚从哪里开始......

Answer 1

你似乎想要generate_series()和join和group by。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：

我看到你想要的日子。这在聚合中稍微有点工作：

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：这不会返回您的确切结果。我认为这些是正确的。

Answer 2

我会考虑range types。使用range operators使计算更简单，更清晰 - 我使用下面的重叠&&和交叉点*。我们可以使用功能性GiST or SP-GiST index快速查询 - 如果表格很大。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 <>小提琴here

请注意，默认情况下，date_range包含一个包含的低位和独占上限。你的范围包括上限和下限，所以用：daterange创建daterange(start_date, end_date, '[]')。函数upper()仍然返回独占上限。因此，表达upper(overlap) - lower(overlap)做正确的计算天数。

有一个原因我使用generate_series()与timestamp输入：

• Generating time series between two dates in PostgreSQL

有关：

• Perform this hours of operation query in PostgreSQL

或者，如果您不想使用范围类型，请考虑使用OVERLAPS运算符：

• Find overlapping date ranges in PostgreSQL