根据其“新记录”更新表“先前记录”

Question

是否有可能根据其machine_id用新行date_start更新前一行date_end ？

机器日志：

record_id   machine_id  date_start  date_end

1           EQPT-1      10-27-2015
2           EQPT-1      10-28-2015      
3           EQPT-2      10-28-2015
4           EQPT-3      10-28-2015
5           EQPT-3      10-30-2015
6           EQPT-2      10-30-2015


UPDATE machine_log 
SET prev.date_end = new.date_start
WHERE new.machine_id = prev.machine_id
AND new.record_id != prev.record_id

Answer 1

如果您使用的是SQL Server 2012或更高版本，则可以使用LEAD功能： SQL Fiddle

UPDATE m
SET m.date_end = lead.endDate
FROM machine_log AS m
INNER JOIN 
(
SELECT 
record_id
, LEAD(date_start) OVER (PARTITION BY machine_id ORDER BY date_start) endDate
FROM machine_log
) AS lead ON m.record_id = lead.record_id

而且，如果您使用的是MySQL，则可以使用Limit来模拟： SQL Fiddle

UPDATE machine_log m
INNER JOIN 
(select 
 record_id, 
 (select b.date_start
  from machine_log b
  where b.machine_id=a.machine_id
    and b.date_start > a.date_start
  order by b.date_start Limit 1) as endDate
  from machine_log a
  order by record_id,date_start) lead
ON m.record_id = lead.record_id
SET m.date_end = lead.endDate
;

Answer 2

如果使用SQL Server：

UPDATE machine_log as next inner join machine_log as prev
on next.machine_id=prev.machine_id
SET prev.date_end = next.date_start
WHERE  next.record_id != prev.record_id