select * from b a1 inner join a a2 on a1.deviceCode=a2.deviceCode where not exists(select 1 from b where a1.deviceCode=deviceCode and a1.gpsTime<gpsTime)
select A.id,cusName,A.deviceCode,gpsTime from A,(select * from B B1 where not exists (select 1 from B where B1.gpsTime<gpsTime))C where A.deviceCode=C.deviceCode
or select * from b a1 inner join a a2 on a1.deviceCode=a2.deviceCode inner join (select deviceCode,max(gpsTime) as ma from b group by deviceCode) c on a1.deviceCode=c.deviceCode and a1.gpsTime=c.ma
请问三楼,在查询分析器里不能执行,提示gpsTime错误。 (select deviceCode,max(gpsTime) as ma from b group by deviceCode)
错误信息,你的代码select deviceCode,max(gpsTime) as ma from b group by deviceCode 没有问题嘛
没看懂。 是不是取最大一条? grpTime应该有索引吧?试试这个select * from b a1 inner join a a2 on a1.deviceCode=a2.deviceCode where gpsTime = (select max(gpsTime) grpTime from b)
inner join a a2 on a1.deviceCode=a2.deviceCode
where not exists(select 1 from b where a1.deviceCode=deviceCode and a1.gpsTime<gpsTime)
from A,(select * from B B1 where not exists (select 1 from B where B1.gpsTime<gpsTime))C
where A.deviceCode=C.deviceCode
select * from b a1
inner join a a2 on a1.deviceCode=a2.deviceCode
inner join (select deviceCode,max(gpsTime) as ma from b group by deviceCode) c
on a1.deviceCode=c.deviceCode and a1.gpsTime=c.ma
(select deviceCode,max(gpsTime) as ma from b group by deviceCode)
没有问题嘛
表B有字段id, gpsTime(datetime), deviceCode(varchar)
deviceCode、gpsTime建立复合索引
[征集]分组取最大N条记录方法征集,及散分....
建议你列出你的表结构,并提供测试数据以及基于这些测试数据的所对应正确结果。
参考一下这个贴子的提问方式http://topic.csdn.net/u/20091130/20/8343ee6a-417c-4c2d-9415-fa46604a00cf.html
1. 你的 create table xxx .. 语句
2. 你的 insert into xxx ... 语句
3. 结果是什么样,(并给以简单的算法描述)
4. 你用的数据库名称和版本(经常有人在MS SQL server版问 MySQL)
这样想帮你的人可以直接搭建和你相同的环境,并在给出方案前进行测试,避免文字描述理解上的误差。
grpTime应该有索引吧?试试这个select * from b a1
inner join a a2 on a1.deviceCode=a2.deviceCode
where gpsTime = (select max(gpsTime) grpTime from b)