MS Access - SQL Query for Average of Each Day Data

问题

I have a set of data spanning across 3 days. Based on the first column from the left, is it possible to have a query that calculates the average of the values in the third column from the left based on each day?

The end result will be two columns:

1/1/2008 | 1.605 
2/1/2008 | 1.59 
3/1/2008 | 1.56

I think the logic will be something like in a loop:

Based on the day in the first column, if it is the same day, count the number of rows and add up the values of the third column
Use the sum of the values of the third column and divide by the number of rows to get the Average
day + 1

But how can we implement a loop in MS Access?

Here is the set of data:

Edit: If I want to group by the date, where the day is between yesterday's 6PM to today's 6PM?

The BETWEEN clause is to check for records that are between yesterday's 18:00:00 and today's 18:00:00. Example, for 1/1/2008, the record will start from 1/1/2008 6:00PM to 2/1/2008 6:00PM. For 2/1/2008, the record will start from 2/1/2008 6:00PM to 3/1/2008 6:00PM`. So on and so forth...

I have a code snippet that checks for this:

([In process analysis result].[Date Time]) Between Date()-1+#12/30/1899 18:0:0# And Date()+#12/30/1899 18:0:0#)

But it only groups for one day before. How can I apply for the set of data?

Edit 2: This is the query that I have done, but it is still not correct. Any idea what is wrong?

SELECT DateValue([Date Time]) As DateValue, Avg([MFR g/10min]) AS [AvgOfMFR g/10min]
FROM [In process analysis result]
WHERE ((([Date Time])>Now()-365) AND (([Operation Grade-Load]) Like "EX*") AND (([Date Time]) Between [Date Time]-1+#12/30/1899 18:0:0# And [Date Time]+#12/30/1899 18:0:0#))
GROUP BY DateValue([Date Time]);

回答1:

SELECT the AVG of the value and GROUP BY the date

回答2:

Your logic looks basically correct. The where clause looks off. Start with this:

SELECT DateValue(DateAdd("h", 6, [Date Time])) As DateValue,
       Avg([MFR g/10min]) AS [AvgOfMFR g/10min]
FROM [In process analysis result]
WHERE [Date Time] > DateAdd("yyyy", -1, DateAdd("h", 6, Now())) AND
      [Operation Grade-Load] Like "EX*" 
GROUP BY DateValue(DateAdd("h", 6, [Date Time]));

I'm not sure what the BETWEEN condition is supposed to be doing. If you want a particular date range, just use date constants.

Edit: Date/time should be offset by 6 hours as in the above edit. And a proper 1-year-back expression should be used. Not sure if current time should be shifted 6 hours too (shown); if not, just remove the DateAdd of Now().

来源：https://stackoverflow.com/questions/41581378/ms-access-sql-query-for-average-of-each-day-data

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sql

ms-access

aggregate-functions

average