mysql - T-SQL 分组/合并记录

Question

我有一个事件表，它包含“开始”和(以及许多其他)“结束”事件。

person, datetime, event
1, 2015-01-1 13:30, start
2, 2015-01-1 13:33, start
3, 2015-01-1 13:38, start
2, 2015-01-1 13:57, end
1, 2015-01-1 14:03, end
1, 2015-01-1 14:07, start
1, 2015-01-1 14:12, end

我希望像这样检索它们:

person, start, end
1, 2015-01-01 13:30, 2015-01-01 14:03
1, 2015-01-01 14:07, 2015-01-01 14:12
2, 2015-01-01 13:33, 2015-01-01 13:57
3, 2015-01-01 13:38, null

我似乎无法将关键字放在一起来找到这种“组合行”机制或类似的场景。

Answer 1

没有子查询

SELECT startevent.person_id as person, 
       startevent.datetime as [start],
       min(endevent.datetime) as [end]
  FROM person_events as startevent 
  join person_events as endevent 
    on startevent.person_id = endevent.person_id 
   and startevent.event = 'start'
   and endevent.event =   'end'
   and startevent.datetime < endevent.datetime
 GROUP BY startevent.person_id, startevent.datetime
 ORDER BY startevent.person_id, startevent.datetime