Question

我正在使用Microsoft Access中分析的表。它有很多字段，但在这种情况下用于过滤的三个字段被分析.readings_miu_id，analyze.ReadDate，analyze.ReadTime。我需要从“已分析”表中提取记录，其中readings_miu_id组合在一起，然后按ReadDate排序，但仅显示所述日期的最后一个条目，这可能是ReadTime中的最高值。我创建了一个查询：

SELECT readings_miu_id, Reading, ReadDate, ReadTime, 
    MIUwindow, SN, Noise, RSSI, OriginCol, ColID, Ownage
FROM analyzed
WHERE analyzed.ReadDate Between #4/21/2009# and #4/29/2009#  
AND analyzed.ReadTime= ( 
    SELECT TOP 1 analyzed.ReadTime 
    FROM analyzed 
    WHERE analyzed.readings_miu_id = *????*** 
    ORDER BY analyzed.ReadTime DESC);

* ???? ***用于表明我不知道该放什么

如果我输入有效的readings_miu_id，我会得到一条记录，其中readings_miu_id的时间最长。

如何使用上面的子查询仅为每个ReadDate读取每个readings_miu_id的最后一个ReadTime？

readings_miu_id 不是表格ID，更类似于项目编号或名称

Answer 1

 SELECT readings_miu_id
    , Reading , ReadDate , ReadTime
    , MIUwindow, SN, Noise, RSSI
    , OriginCol, ColID, Ownage 
 FROM analyzed AS A
    WHERE analyzed.ReadDate Between #4/21/2009# and #4/29/2009# 
       AND analyzed.ReadTime=
          (SELECT TOP 1 analyzed.ReadTime FROM analyzed 
             where analyzed.readings_miu_id = A.readings_miu_id 
                AND analyzed.ReadDate = A.ReadDate
             ORDER BY analyzed.ReadTime DESC);

我把主表别名为A，并在子查询中引用它。不确定是否需要按子查询中的“读取日期”进行过滤。

Answer 2

这会让你接近。声明“readings_miu_id组合在一起”让我很困惑。不确定是否需要GroupBy或该字段的排序。此查询将为您提供分析表中具有相同日期但是该给定日期的“最大：”时间的记录。听起来像是你想要的。

SELECT readings_miu_id, Reading, ReadDate, ReadTime, MIUwindow, SN, Noise, RSSI, OriginCol, ColID, Ownage 
FROM analyzed ,
(
  Select ReadDate as matchDate, Max(ReadTime) as matchTime
  FROM analyzed 
  Where analyzed.ReadDate Between #4/21/2009# and #4/29/2009# 
  Group by ReadDate
) dateAndTime
WHERE analyzed.ReadDate Between #4/21/2009# and #4/29/2009# AND ReadDate = dateAndTime.matchDate AND readTime = dateAndTime.matchTime  
Order By readDate

MS ACCESS中的子查询：每个日期每个“人”只选择一条记录

2 个答案: