MS ACCESS 中的子查询：每个日期每个“人”只选择一条记录

Question

我在 Microsoft Access 中使用了一个名为已分析的表。它有很多字段，但在这种情况下用于过滤的三个字段是analyzed.readings_miu_id、analyzed.ReadDate、analyzed.ReadTime。我需要从“已分析”表中提取记录，其中将 readings_miu_id 分组在一起，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 中的最高值时间。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);

*????*** 被用来表明我不知道该放什么

如果我输入了一个有效的 readings_miu_id，我会得到一条该 readings_miu_id 时间最长的记录。

我如何使用像上面这样的子查询来仅提取每个 ReadDate 每个 readings_miu_id 的最后一个 ReadTime？

readings_miu_id不是表ID，更像是Item Number或Name

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);

我只是将主表别名为 A 并在子查询中引用它。不确定是否需要在子查询中按 ReadDate 进行过滤。

Answer 2

这会让你接近。 “将 readings_miu_id 组合在一起”的说法让我感到困惑。不确定您是否需要 GroupBy 或对该字段进行排序。此查询将为您提供分析表中具有相同日期的记录，但该给定日期的“最大：”时间。听起来这就是你想要的。

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