有下列表数据
dataId tm v
21 2012/12/1 00:00:00 13
21 2012/12/1 01:00:00 12
22 2012/12/1 00:00:00 3
22 2012/12/1 01:00:00 1
23 2012/12/1 00:00:00 5
23 2012/12/1 01:00:00 6
24 2012/12/1 00:00:00 7
24 2012/12/1 01:00:00 8
写一条sql语句查询如下结果该怎么写？
tm v1 v2 v3 v4
2012/12/1 00:00:00 13 3 5 7
2012/12/1 01:00:00 12 1 6 8
sql
------解决方案--------------------------------------------------------
竖转横
select tm,
max(case when dataid=21 then v else null end) as v1,
max(case when dataid=22 then v else null end) as v2,
max(case when dataid=23 then v else null end) as v3,
max(case when dataid=24 then v else null end) as v4
from 表名
group by tm