SubQueries in MS ACCESS: selecting only one record per “person” per date

StackOverflow https://stackoverflow.com/questions/883383

Question

I am using a table called analyzed in Microsoft Access. It has many fields but the three ones being used for filtering in this case are analyzed.readings_miu_id, analyzed.ReadDate, analyzed.ReadTime. I need to pull the records from the "analyzed" table where readings_miu_id are grouped together then sorted by ReadDate but showing only the last entry for said date which could be the highest valued time in ReadTime. I've created a query:

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);

*????*** is being used to show that im not sure what to put here

if i enter in a valid readings_miu_id i get one record with the highest time for that readings_miu_id.

How do i use a sub query like the one above to pull only the last ReadTime per readings_miu_id per ReadDate?

readings_miu_id is not the table ID, it is more similar to an Item Number or a Name

Was it helpful?

Solution 

 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);

I just aliased the main table as A and just refered to it in the subquery. Not sure if you need to filter by ReadDate in your subquery.

OTHER TIPS

this will get you close. The statement "where readings_miu_id are grouped together" is confusing me. not sure if you want a GroupBy or a sort on that field. This query will give youthe records from your analyzed table that have the same date, but the "biggest:" time for that given date. Sounds like it's what you wanted.

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
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