求帮助，oracle数据库，查询出每个最新时间的那一条数据

Question

select p.* from (select rownum as 序号 ,n.* from (select sitename as 站点名称, RecordTime as 记录时间 ,decode(avg(case item when 211 then value else null end),0,'0.00000',trim(to_char(avg(case item when 211 then value else null end),'99999999999990.99999'))) "SO2(mg/m3)" from(select s.sitename,m.* from air_temphourdata m left join site s on m.sitecode=s.sitecode where m.SiteCode in ('34656-31102001','34656-31102006'))group by sitename,Recordtime having to_char(Recordtime,'yyyymmddhhmmss')=MAX(to_char(Recordtime,'yyyymmddhhmmss')) order by RecordTime desc ) n )p where p.序号 between 1 and 15 只查询出每个站点最大时间的那一条

Answer 1

很简单的问题，使用窗口函数解决~
select 站点名称,first_value("SO2(mg/m3)") over(partition by 站点名称 order by 记录时间 desc)
from (
select sitename as 站点名称,
RecordTime as 记录时间,
decode(avg(case item
when 211 then
value
else
null
end),
0,
'0.00000',
trim(to_char(avg(case item
when 211 then
value
else
null
end),
'99999999999990.99999'))) "SO2(mg/m3)"
from (select s.sitename, m.*
from air_temphourdata m
left join site s
on m.sitecode = s.sitecode
where m.SiteCode in ('34656-31102001', '34656-31102006'))) n