[英]How do I write a Query to join two tables based on minimum absolute time difference?
I need help writing a MySQL query to do a matching with the tables below.我需要帮助编写 MySQL 查询来匹配下表。 So far my query looks like this:
到目前为止,我的查询如下所示:
SELECT event.id, event.eventid, upload.uploadid
FROM event
LEFT JOIN upload
ON(event.id = upload.id and event.timestamp <= upload.timestamp);
The second condition in my join, event.timestamp <= upload.timestamp
, is a placeholder until I can figure out a boolean expression (or something else) to get the desired result.我的加入中的第二个条件
event.timestamp <= upload.timestamp
是一个占位符,直到我可以找出 boolean 表达式(或其他表达式)以获得所需的结果。 I'm lost on how to write a statement to join based on minimum absolute time difference.我不知道如何根据最小绝对时间差编写加入声明。 The tables have the following structure:
这些表具有以下结构:
Event table事件表
id ![]() |
eventid![]() |
timestamp![]() |
---|---|---|
u1 ![]() |
event1![]() |
2020-01-01 01:30:00 ![]() |
u1 ![]() |
event2![]() |
2020-01-01 01:45:00 ![]() |
u2 ![]() |
event1![]() |
2020-01-01 05:30:00 ![]() |
u2 ![]() |
event2![]() |
2020-01-01 05:39:00 ![]() |
Upload table上传表格
id ![]() |
uploadid![]() |
timestamp![]() |
---|---|---|
u1 ![]() |
upload1![]() |
2020-01-01 01:30:00 ![]() |
u1 ![]() |
upload2![]() |
2020-01-01 02:30:00 ![]() |
u2 ![]() |
upload1![]() |
2020-01-01 05:30:00 ![]() |
u2 ![]() |
upload2![]() |
2020-01-01 05:35:00 ![]() |
The query needs to match every event in the event table to the closest upload from that respective user.查询需要将事件表中的每个事件与来自该相应用户的最近上传相匹配。
The desired result of the query is:查询的期望结果是:
u1 event1 upload1
u1 event2 upload1
u2 event1 upload1
u2 event2 upload2
EDIT: The following query produced the the desired result:编辑:以下查询产生了所需的结果:
SELECT e.id, e.eventid,
(SELECT u.uploadid
FROM upload u
WHERE (u.id = e.id and u.timestamp < e.timestamp)
ORDER BY ABS(TIMESTAMPDIFF(second, u.timestamp, e.timestamp))
LIMIT 1)
FROM event e;
If you only want the uploadid
, then I would suggest a correlated subquery:如果您只想要
uploadid
,那么我建议使用相关子查询:
SELECT e.*,
(SELECT u.uploadid
FROM upload u
WHERE u.id = e.id
ORDER BY ABS(TIMESTAMPDIFF(second, e.timestamp, u.timestamp))
) as uploadid
FROM event e;
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