SQL/Postgres 日期时间划分/规范化答案

【问题标题】：SQL/Postgres datetime division / normalizingSQL/Postgres 日期时间划分/规范化
【发布时间】：2014-12-10 10:41:52
【问题描述】：

我有这个活动表

+--------------+------------------+
| Field        | Type             |
+--------------+------------------+
| id           | int(11) unsigned |
| start_date   | timestamp        |
| end_date     | timestamp        |
| ...          |                  |
+--------------+------------------+

我需要一个视图，该视图按 start_date 按 DAY 对这些活动进行分组，但如果 end_date 与 start_date 不在同一天，则视图会再次包含条目，但 start_date 设置为 00:00第二天..（依此类推，根据需要重复多次，直到 start_date 与 end_date 在同一天）

举个例子：

如果活动表包含：

+--------------+----------------------------+----------------------------+
| id           | start_date                 | end_date                   |
+--------------+----------------------------+----------------------------+
|  1           | 2014-12-02 14:12:00+00     | 2014-12-03 06:45:00+00     |   
|  2           | 2014-12-05 15:25:00+00     | 2014-12-05 07:29:00+00     |                                
+--------------+----------------------------+----------------------------+

视图应包含：

+--------------+----------------------------+----------------------------+
| activity_id  | start_date                 | end_date                   |
+--------------+----------------------------+----------------------------+
|  1           | 2014-12-02 14:12:00+00     | 2014-12-02 23:59:59+00     |   
|  1           | 2014-12-03 00:00:00+00     | 2014-12-03 06:45:00+00     |
|  2           | 2014-12-05 15:25:00+00     | 2014-12-05 07:29:00+00     |                                  
+--------------+----------------------------+----------------------------+

任何帮助将不胜感激！

PS：我正在使用 postgresql

【问题讨论】：

标签： sql database postgresql datetime views

【解决方案1】：

要获取所需的行，首先使用set returning function 和lateral join。从那里，使用CASE 语句和date arithmetics 提取相关值。

下面是一个帮助您入门的示例：

with data as (
  select id, start_date, end_date
  from (values
    (1, '2014-12-02 14:12:00+00'::timestamptz, '2014-12-03 06:45:00+00'::timestamptz),
    (2, '2014-12-05 15:25:00+00'::timestamptz, '2014-12-05 07:29:00+00'::timestamptz)
  ) as rows (id, start_date, end_date)
)
select data.id,
      case days.d = date_trunc('day', data.start_date)
        when true then data.start_date
        else days.d
      end as start_date,
      case days.d = date_trunc('day', data.end_date)
        when true then data.end_date
        else days.d + interval '1 day' - interval '1 sec'
      end as end_date
from data
join generate_series(
      date_trunc('day', data.start_date),
      date_trunc('day', data.end_date),
      '1 day'
      ) as days (d)
      on days.d >= date_trunc('day', data.start_date)
      and days.d <= date_trunc('day', data.end_date)

 id |       start_date       |        end_date        
----+------------------------+------------------------
  1 | 2014-12-02 15:12:00+01 | 2014-12-02 23:59:59+01
  1 | 2014-12-03 00:00:00+01 | 2014-12-03 07:45:00+01
  2 | 2014-12-05 16:25:00+01 | 2014-12-05 08:29:00+01
(3 rows)

顺便说一句，根据你在做什么，使用date range 可能更有意义：

with data as (
  select id, start_date, end_date
  from (values
    (1, '2014-12-02 14:12:00+00'::timestamptz, '2014-12-03 06:45:00+00'::timestamptz),
    (2, '2014-12-05 07:25:00+00'::timestamptz, '2014-12-05 15:29:00+00'::timestamptz)
  ) as rows (id, start_date, end_date)
)
select data.id,
      tstzrange(data.start_date, data.end_date)
from data;

 id |                      tstzrange                      
----+-----------------------------------------------------
  1 | ["2014-12-02 15:12:00+01","2014-12-03 07:45:00+01")
  2 | ["2014-12-05 08:25:00+01","2014-12-05 16:29:00+01")
(2 rows)

【讨论】：