SqlServer 开窗函数实例

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目标：我要统计项目工作量。
梳理：项目有多个钻孔，钻孔有多个回次。先找到每个钻孔的回次最大深度，再求和。
解题：

1.找到各个钻孔最深的记录

select ZKBH,MAX(CAST(JSSD as FLOAT)) as Depth 
from ZKHCXX  where zkbh in (select zkbh from  ZKXX where oaid = 'xxx')
GROUP BY ZKBH

2.求和

select Sum(Depth) from (
  select ZKBH,MAX(CAST(JSSD as FLOAT)) as Depth 
  from ZKHCXX  where zkbh in (select zkbh from  ZKXX where oaid = 'xxx')
  GROUP BY ZKBH
)

3.纳尼！语法错误。显然不能把 group by 包到查询中，说明此路不同。

> [42000] [Microsoft][SQL Server Native Client 11.0][SQL Server]')' 附近有语法错误。 (102)

4.开窗函数出马，一个顶俩。

select Sum(depth) from
(
  select 
    row_number() over(partition by ZKBH order by cast(JSSD AS FLOAT) desc) as rn,
    CAST(JSSD as FLOAT) as depth
  from ZKHCXX  where zkbh in (select zkbh from  ZKXX where oaid = 'xxx')
) t
where t.rn = 1