一系列日期的最近记录

本文介绍了一系列日期的最近记录的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 我知道要获取日期之前的最近记录，我可以使用查询：I know that to get the closest record prior to a date I can use the query:select *from resultswhere resulttime = (select max(resulttime) from results where some_id = 15 and resulttime < '2012-07-27');但是我需要连续几天这样做，以便我知道每个记录的最近记录天。有什么想法吗？But I need to do this for a series of days, so that I know the closest record for each day. Any ideas?一系列的日子将由 generate_sequence（）生成。The series of days would be generated by generate_sequence().最接近的先前记录可能在我们想要其值的前一天，但仍需要返回。The closest prior record may be in a prior day to what we want the value for, but still need to be returned.推荐答案应该最简单& 左联接和 DISTINCT ON 最快：Should be simplest & fastest with a LEFT JOIN and DISTINCT ON:WITH x(search_ts) AS ( VALUES ('2012-07-26 20:31:29'::timestamp) -- search timestamps ,('2012-05-14 19:38:21') ,('2012-05-13 22:24:10') )SELECT DISTINCT ON (x.search_ts) x.search_ts, r.id, r.resulttimeFROM xLEFT JOIN results r ON r.resulttime <= x.search_ts -- smaller or same-- WHERE some_id = 15 -- some condition?ORDER BY x.search_ts, r.resulttime DESC;结果（虚拟值）：search_ts | id | resulttime--------------------+--------+----------------2012-05-13 22:24:10 | 404643 | 2012-05-13 22:24:102012-05-14 19:38:21 | 404643 | 2012-05-13 22:24:102012-07-26 20:31:29 | 219822 | 2012-07-25 19:47:44我使用 CTE 来提供值，可以是表或函数或非嵌套数组或由 generate_series（） 以及其他内容。 （您是说 generate_series（）的意思是 generate_sequence（）吗？）I use a CTE to provide the values, could be a table or function or unnested array or a set generated with generate_series() something else as well. (Did you mean generate_series() by "generate_sequence()"?)第一个我 JOIN 搜索时间戳到表中所有具有或更早 resulttime 的行。我使用 LEFT JOIN 代替 JOIN ，以便在没有先前的结果时间完全在表中。First I JOIN the search timestamps to all rows in the table with earlier or equal resulttime. I use LEFT JOIN instead of JOIN so that search timestamps are not dropped when there is no prior resulttime in the table at all.在 DISTINCT ON（x.search_ts）与 ORDER BY x.search_ts，r.resulttime DESC 结合，我们得到最大的（或同等最大的一个） resulttime 小于或等于每个搜索时间戳。With DISTINCT ON (x.search_ts) in combination with ORDER BY x.search_ts, r.resulttime DESC we get the greatest (or one of the equally greatest) resulttime that is smaller or equal to each search timestamp. 这篇关于一系列日期的最近记录的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！