[英]Selecting ranges of dates without overlapping
我有以下關系模式:
dates(date: date, code: char)
代碼可以是ST,MN,MX,ED。 一個例子:
╔════════════╦══════╗
║ date ║ code ║
╠════════════╬══════╣
║ 2001-10-01 ║ ST ║
║ 2001-10-20 ║ ST ║
║ 2001-11-01 ║ MX ║
║ 2001-11-01 ║ MN ║
║ 2001-11-14 ║ MX ║
║ 2001-11-15 ║ ED ║
║ 2001-11-15 ║ MX ║
║ 2001-11-27 ║ MN ║
║ 2001-12-01 ║ ST ║
║ 2001-12-01 ║ ED ║
║ 2001-12-02 ║ MX ║
║ 2001-12-03 ║ MX ║
║ 2001-12-05 ║ ED ║
║ 2001-12-20 ║ ST ║
║ 2001-12-21 ║ MN ║
║ 2001-12-24 ║ MX ║
║ 2001-12-31 ║ ED ║
╚════════════╩══════╝
我需要:
我通過以下查詢完成了第一部分:
SELECT DISTINCT ON (dt.date) dt.date AS start, dt1.date AS end
FROM dates AS dt, dates AS dt1
WHERE dt.type='ST' AND dt1.type='ED' AND dt.date<dt1.date;
我不知道如何消除重疊范圍。 使用給定的示例數據,我的查詢輸出:
╔════════════╦════════════╗
║ start ║ end ║
╠════════════╬════════════╣
║ 2001-10-01 ║ 2001-12-01 ║
║ 2001-10-20 ║ 2001-11-15 ║
║ 2001-12-01 ║ 2001-12-31 ║
║ 2001-12-20 ║ 2001-12-31 ║
╚════════════╩════════════╝
如您所見,第二個范圍與第一個范圍重疊,因此它無法正常工作。
正確的輸出應為:
╔════════════╦════════════╗
║ start ║ end ║
╠════════════╬════════════╣
║ 2001-10-20 ║ 2001-11-15 ║
║ 2001-12-20 ║ 2001-12-31 ║
╚════════════╩════════════╝
如果我理解正確的話,那么你可以使用lead()
並where
為了這個目的:
select date as startdate, next_date as enddate
from (select d.*,
lead(code) over (order by date) as next_code,
lead(date) over (order by date) as next_date
from dates d
where code in ('ST', 'ED')
) d
where code = 'ST' and
next_code = 'ED';
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