Question

伙计我有两个名为Requisition和RequisitionHistory的表。表Requisition是唯一条目，其中唯一条目基于RequisitionCode（PK），但表RequisitionHistory中有多行基于RequisitionCode因为每次都有Requisition在RequisitionHistory表上执行任何操作（例如更新等），在Requisiton中插入新条目。

这是我的+-----------------+---------------+--------------------+ | RequisitionCode | ApprovedCount | RequisitionDate | +-----------------+---------------+--------------------+ | 1 | 10 | 02/01/2014 | | 2 | 23 | 01/01/2014 | | 3 | 3 | 02/01/2014 | +-----------------+---------------+--------------------+表

RequisitionHistory

这是我的+------------------------+-----------------+---------------+-----------------+ | RequisitionHistoryCode | RequisitionCode | ApprovedCount | RequisitionDate | +------------------------+-----------------+---------------+-----------------+ | 1 | 1 | 14 | 01/01/2014 | | 2 | 1 | 10 | 02/01/2014 | | 3 | 2 | 23 | 01/01/2014 | | 4 | 3 | 1 | 01/01/2014 | | 5 | 3 | 3 | 02/01/2014 | +------------------------+-----------------+---------------+-----------------+表

RequisitionDate

这些表中还有其他列，但是对于我的查询，它们是无关的，因此它们不包括在内。

现在我要做的是从ApprovedCount获取每个RequisitionCode的最新信息（基于RequisitionHistory）ApprovedCount，然后从RequisitionCode中删除它相同RequisitionCode的第二个最后一个条目（RequisitionHistory中select RequisitionCode , (ISNULL((select top 1 ApprovedCount from RequisitionHistory where RequisitionCode =r.RequisitionCode order by RequisitionDate desc),0) - ISNULL( (select top 1 ApprovedCount from RequisitionHistory where RequisitionCode NOT IN (select top 1 ApprovedCount from RequisitionHistory where RequisitionCode =r.RequisitionCode order by RequisitionDate desc) and RequisitionCode = r.RequisitionCode order by RequisitionDate DESC),0)) as StructureChange from Requisition r可能有一个或多个条目

我试图做什么（但悲惨地失败）

{{1}}

我做错了什么？

Answer 1

尝试此操作后会得到什么：

select RequisitionCode ,
(
ISNULL((select top 1 ApprovedCount from RequisitionHistory rh
where rh.RequisitionCode =r.RequisitionCode order by rh.RequisitionDate desc),0)
-
ISNULL(
(select top 1 ApprovedCount from RequisitionHistory rh1 where rh1.RequisitionHistoryCode
NOT IN 
  (select top 1 RequisitionHistoryCode from RequisitionHistory rh2 
    where rh2.RequisitionCode =r.RequisitionCode order by rh2.RequisitionDate desc) 
  and rh1.RequisitionCode = r.RequisitionCode order by rh1.RequisitionDate DESC),0))
as StructureChange 
from Requisition r

Answer 2

在Sql Server中，您可以用稍微更易读的方式来完成它：

    WITH AprovalRecency AS (
    SELECT RequisitionCode, ApprovedCount, 
      RANK () OVER (PARTITION BY RequisitionCode 
                    ORDER BY RequisitionHistoryCode DESC) as Recency
    FROM RequisitionHistory 
    WHERE)
    SELECT r.*,  COALESCE(ar2.ApprovedCount, 0) - COALESCE(ar1.ApprovedCount, 0)
    FROM Requisition r LEFT JOIN 
     AprovalRecency ar1 ON r.RequisitionCode  = ar1.RequisitionCode 
                         AND ar1.Recency = 1 LEFT JOIN 
    AprovalRecency ar2 ON r.RequisitionCode  = ar2.RequisitionCode 
                         AND ar2.Recency = 2

如何从同一个表中的另一行中减去一行？

2 个答案: