需求 查询小时气象表中 同一日期、同一城市、同意检测站点 首要污染物出现次数最多的记录
第一步: 添加 排序字段
select StationID,RecordDate,CityID,Primary_Pollutant,ROW_NUMBER() over(partition by StationID,RecordDate,CityID order by count(0) desc ) as Numfrom T_AirHourly
group by StationID,RecordDate,CityID,Primary_Pollutant
第二步 子查询:在查询的基础上再次查询
select StationID,RecordDate,CityID,Primary_Pollutant from (
select StationID,RecordDate,CityID,Primary_Pollutant,ROW_NUMBER() over(partition by StationID,RecordDate,CityID order by count(0) desc ) as Numfrom T_AirHourly
group by StationID,RecordDate,CityID,Primary_Pollutant
)t where t.Num = 1
第三步 创建视图
create view V_Primary_Pollutant as
select StationID,RecordDate,CityID,Primary_Pollutant from (
select StationID,RecordDate,CityID,Primary_Pollutant,ROW_NUMBER() over(partition by StationID,RecordDate,CityID order by count(0) desc ) as Numfrom T_AirHourly
group by StationID,RecordDate,CityID,Primary_Pollutant
)t where t.Num = 1
结果:
第五步: 统计一天中各种污染物的平均值
将视图作为独立模块 左连接查询 统计一天 各种污染物的平均值。
转载:
row_ number over函数的基本用法
https://xiaoxiaoher.iteye.com/blog/2428619