PostgreSQL:在事件中分割时间段 [英] postgresql: splitting time period at event
问题描述
我有一张国家时期表。在某些情况下,某些国家/地区属性(例如首都)会在一段时间内的某个日期发生变化。在这里,我想将国家/地区时段分为两个新时期,一个是此变更之前,另一个是变更之后。
I have a table of country-periods. In some cases, certain country attributes (e.g. the capital) changes on a date within a time period. Here I would like to split the country-period into two new periods, one before and one after this change.
示例:
Country | start_date | end_date | event_date
A | 1960-01-01 | 1999-12-31 | 1994-07-20
B | 1926-01-01 | 1995-12-31 | NULL
所需的输出:
Country | start_date | end_date | event_date
A | 1960-01-01 | 1994-07-19 | 1994-07-20
A | 1994-07-20 | 1999-12-31 | 1994-07-20
B | 1926-01-01 | 1995-12-31 | NULL
我考虑从 generate_series 开始,遵循以下原则:
I considered starting off with generate_series along these lines:
SELECT country, min(p1) as sdate1, max(p1) as sdate2,
min(p2) as sdate2, min(p2) as edate2
FROM
(SELECT country,
generate_series(start_date, (event_date-interval '1 day'), interval '1 day')::date as p1,
generate_series(event_date, end_date, interval '1 day')::date as p2
FROM table)t
GROUP BY country
但是这些似乎导致效率低下和混乱。不幸的是,我在编写函数方面没有任何经验。关于如何解决此问题的任何想法吗?
But these seems way to inefficient and messy. Unfortunately I don't have any experience when it comes to writing functions. Any ideas on how I can solve this?
推荐答案
您可以执行 UNION
代替。这样,您就不会生成不必要的行
You can do UNION
instead. This way you don't generate unnecessary rows
SELECT country, start_date,
CASE WHEN event_date BETWEEN start_date AND end_date
THEN event_date - 1
ELSE end_date
END AS end_date, event_date
FROM table1
UNION ALL
SELECT country, event_date, end_date, event_date
FROM table1
WHERE event_date BETWEEN start_date AND end_date
ORDER BY country, start_date, end_date, event_date
这是一个 SQLFiddle 演示
输出:
| country | start_date | end_date | event_date |
|---------|------------|------------|------------|
| A | 1960-01-01 | 1994-07-19 | 1994-07-20 |
| A | 1994-07-20 | 1999-12-31 | 1994-07-20 |
| B | 1926-01-01 | 1995-12-31 | (null) |
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