将 MySQL join 返回的结果限制为 1

Question

我正在对两个表进行 JOIN，右侧有多个 ON 子句的结果：e.ID = ti.event_id。如何将连接返回的结果限制为 1？有点像 LIMIT 1

events_detail tbl:

ID | event_code
---------------
1  | 123-abc
2  | 234-bcd
3  | 345-cde

events_start_end tbl:

id | event_id | start_time | end_time
-------------------------------------
1  | 1        | 12:00      | 17:00
2  | 1        | 13:00      | 15:00
3  | 2        | 12:00      | 15:00
4  | 3        | 07:00      | 10:00
5  | 3        | 08:00      | 11:00

当前查询：

SELECT e.ID, e.event_code, ti.start_time, ti.end_time 
FROM events_detail AS e 
LEFT JOIN events_start_end AS ti 
  ON e.ID = ti.event_id 
WHERE e.event_status = 'A';

实际结果：

ID | event_code | start_time | end_time
---------------------------------------
1  | 123-abc    | 12:00      | 17:00
1  | 123-abc    | 13:00      | 15:00
2  | 234-bcd    | 12:00      | 15:00
3  | 345-cde    | 07:00      | 10:00
3  | 345-cde    | 08:00      | 11:00

首选结果：

ID | event_code | start_time | end_time
---------------------------------------
1  | 123-abc    | 12:00      | 17:00
2  | 234-bcd    | 12:00      | 15:00
3  | 345-cde    | 07:00      | 10:00

Answer 1

使用ROW_NUMBER():

SELECT e.*
FROM (SELECT e.ID, e.event_code, ti.start_time, ti.end_time,
             ROW_NUMBER() OVER (PARTITION BY e.event_code ORDER BY t1.start_time) as seqnum 
      FROM events_detail e LEFT JOIN
           events_start_end ti 
           ON e.ID = ti.event_id 
      WHERE e.event_status = 'A'
     ) e
WHERE seqnum = 1;

Answer 2

我最终使用子查询解决了这个问题：

SELECT `e`.`ID`, 
       `e`.`event_code`, 
       `ti`.`start_time`, 
       `ti`.`end_time` 
FROM `events_detail` AS `e` 
LEFT JOIN `events_start_end` AS `ti` 
    ON `ti`.`id` = (
        SELECT `id` 
        FROM `events_start_end` 
        WHERE `events_start_end`.`event_id` = `e`.`ID` 
        LIMIT 1
    ) 
WHERE `e`.`event_status` = 'A'

将 MySQL join 返回的结果限制为 1

Limit the results returned by MySQL join to 1

mysql

sql

join

limit

greatest-n-per-group