Tableau - Calculating average where date is less than value from another data source

问题

I am trying to calculate the average of a column in Tableau, except the problem is I am trying to use a single date value (based on filter) from another data source to only calculate the average where the exam date is <= the filtered date value from the other source.

Note: Parameters will not work for me here, since new date values are being added constantly to the set.

I have tried many different approaches, but the simplest was trying to use a calculated field that pulls in the filtered exam date from the other data source.

It successfully can pull the filtered date, but the formula does not work as expected. 2 versions of the calculation are below:

IF DATE(ATTR([Exam Date])) <= DATE(ATTR([Averages (Tableau Test Scores)].[Updated])) THEN AVG([Raw Score]) END

IF DATEDIFF('day', DATE(ATTR([Exam Date])), DATE(ATTR([Averages (Tableau Test Scores)].[Updated]))) > 1 THEN AVG([Raw Score]) END

Basically, I am looking for the equivalent of this in SQL Server:

SELECT AVG([Raw Score]) WHERE ExamDate <= (Filtered Exam Date)

Below a workbook that shows an example of what I am trying to accomplish. Currently it returns all blanks, likely due to the many-to-one comparison I am trying to use in my calculation.

Any feedback is greatly appreciated!

Tableau Test Exam Workbook

回答1:

I was able to solve this by using Custom SQL to join the tables together and calculate the average based on my conditions, to get the column results I wanted.

Would still be great to have this ability directly in Tableau, but whatever gets the job done.

Edit:

SELECT 
[AcademicYear]
,[Discipline]
--Get the number of student takers
,COUNT([Id]) AS [Students (N)]
--Get the average of the Raw Score
,CAST(AVG(RawScore) AS DECIMAL(10,2)) AS [School Mean]
--Get the number of failures based on an "adjusted score" column
,COUNT([AdjustedScore] < 70 THEN 1 END) AS [School Failures]
--This is the column used as the cutoff point for including scores
,[Average_Update].[Updated]
FROM [dbo].[Average] [Average]

FULL OUTER JOIN [dbo].[Average_Update] [Average_Update] ON ([Average_Update].[Id] = [Average].UpdateDateId)

--The meat of joining data for accurate calculations
FULL OUTER JOIN (
SELECT DISTINCT S.[Id], S.[LastName], S.[FirstName], S.[ExamDate], S.[RawScoreStandard], S.[RawScorePercent], S.[AdjustedScore], S.[Subject], P.[Id] AS PeriodId
FROM [StudentScore] S
FULL OUTER JOIN
(
--Get only the 1st attempt
SELECT DISTINCT [NBOMEId], S2.[Subject], MIN([ExamDate]) AS ExamDate
FROM [StudentScore] S2
GROUP BY [NBOMEId],S2.[Subject]
) B
ON S.[NBOMEId] = B.[NBOMEId] AND S.[Subject] = B.[Subject] AND S.[ExamDate] = B.[ExamDate]
--Group in "Exam Periods" based on the list of periods w/ start & end dates in another table.
FULL OUTER JOIN [ExamPeriod] P 
ON  S.[ExamDate] = P.PeriodStart AND S.[ExamDate] <= P.PeriodEnd
WHERE S.[Subject] = B.[Subject]
GROUP BY P.[Id], S.[Subject], S.[ExamDate], S.[RawScoreStandard], S.[RawScorePercent], S.[AdjustedScore], S.[NBOMEId], S.[NBOMELastName], S.[NBOMEFirstName], S.[SecondYrTake]) [StudentScore]  
ON 
([StudentScore].PeriodId = [Average_Update].ExamPeriodId 
AND [StudentScore].Subject = [Average].Subject 
AND [StudentScore].[ExamDate] <= [Average_Update].[Updated])
--End meat


--Joins to pull in relevant data for normalized tables
FULL OUTER JOIN [dbo].[Student] [Student] ON ([StudentScore].[NBOMEId] = [Student].[NBOMEId])
INNER JOIN [dbo].[ExamPeriod] [ExamPeriod] ON ([Average_Update].ExamPeriodId = [ExamPeriod].[Id])
INNER JOIN [dbo].[AcademicYear] [AcademicYear] ON ([ExamPeriod].[AcademicYearId] = [AcademicYear].[Id])

--This will pull only the latest update entry for every academic year.
WHERE [Updated] IN (
SELECT DISTINCT MAX([Updated]) AS MaxDate
FROM [Average_Update]
GROUP BY[ExamPeriodId])

GROUP BY [AcademicYear].[AcademicYearText], [Average].[Subject], [Average_Update].[Updated], 
ORDER BY [AcademicYear].[AcademicYearText], [Average_Update].[Updated], [Average].[Subject]

回答2:

I couldn't download your file to test with your data, but try reversing the order of taking the average ie

average(IF DATE(ATTR([Exam Date])) <= DATE(ATTR([Averages (Tableau Test Scores)].[Updated]) then [Raw Score]) END)

as written, I believe you'll be averaging the data before returning it from the if statement, whereas you want to return the data, then average it.

来源：https://stackoverflow.com/questions/34753054/tableau-calculating-average-where-date-is-less-than-value-from-another-data-so

标签

tableau