Get the Max value of each group in SQL

It looks like you're trying to count the file names. You can get there with this:

SELECT [FileName], count(*) as [FileCount]
FROM PlacedOrderDetails
WHERE CreatedDate >= '12/21/2012'
GROUP BY [FileName]

I need Max FileCount, Group by FileName

FileName     FileCount

ABC                1
ABC                2
ABC                3
DEF                 1
GHI                 1
GHI                  2

So, expected results are

FileName     FileCount

ABC                3
DEF                 1
GHI                  2

please check this article:
https://www.experts-exchange.com/Database/Miscellaneous/A_3203-DISTINCT-vs-GROUP-BY-and-why-does-it-not-work-for-my-query.html
it explains exactly how to do this

To find the max value, this should do the trick

SELECT [FileName], Max(FileCount) as [FileCount]
FROM PlacedOrderDetails
WHERE CreatedDate >= '12/21/2012'
GROUP BY [FileName]

@sjwales

I tried your query in the very first attempt, before posting over here.

I have around 8 - 9 columns

Group by expect all the columns to be mentioned.

On doing so, we don't get the MAX (FileCount)

chokka, did you try the code I posted?
It will work without the cte, and should give you the max file count (by way of counting all the files with the same name).

If I've misunderstood your problem, my apologies.

Is FileCount unique for each occurrence of FileName ?  If so this might work:

Select othercol1, othercol2, otherco3, FileName, FileCount
from
(
SELECT [FileName], Max(FileCount) as [FileCount]
FROM PlacedOrderDetails
WHERE CreatedDate >= '12/21/2012'
GROUP BY [FileName] 
) as a
join PlacedOrderDetails b on a.FileName = b.FileName and a.FileCount = b.FileCount

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Even if it's not unique you could change

Select othercol1, othercol2, otherco3, FileName, FileCount

to

Select DISTINCT othercol1, othercol2, otherco3, FileName, FileCount

Would that work ?

You are correct, you have to enumerate any column not part of an aggregate (min, max, sum, avg, count) in GROUP BY.
That makes sense, because the DBMS cannot decide what you want to see as single values if you have not included them in the GROUP BY. You can for example decide to use the minimum of each other column:

select FileName, min([Trade Name]), min([Invoice Number]), min([Invoice Date]), max(FileCount)
from PlacedOrderDetails
where CreatedDate >= '12/21/2012'

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or you want to have the record with the highest FileCount for each FileName, and then the CTE would come into play.

So, you will need to define exactly what result you want to get, including the other columns.

For all the experts for your query suggestion,

Group by is expecting all the columns which i mentioning in the select query.

On providing all the columns in the Group by, i am not able to get the generated value !!

this will do (as by my article), based on your code:

With CTE
As
(
select

                        [FileName],
                        [Trade Name],
                        [Invoice Number],
                        [Invoice Date]
                        ,ROW_NUMBER() OVER(PARTITION BY [FileName] ORDER BY [Invoice Date] ASC) AS FileCount
,ROW_NUMBER() OVER(PARTITION BY [FileName] ORDER BY [Invoice Date] DESC) AS rn
from                  PlacedOrderDetails
where                  CreatedDate >= '12/21/2012'
)
select
                        [FileName],
                        [Trade Name],
                        [Invoice Number],
                        [Invoice Date]
                        
From                  CTE
WHERE rn = 1

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Can you provide some sample data and the expected output? I suspect the solution will utilize a window function such as row_number() as you have shown in your cte expression, but such functions also include count() and max() which might better provide a solution.

@angelIII
 

select
                        [FileName],
                        [Trade Name],
                        [Invoice Number],
                        [Invoice Date]
                       
From                  CTE


We are missing the FileCount.
I included, but FileCount reflected as FileCount= 1.


We need MAX(FileCount)

I don't believe what your trying to do is uncommon or complicated. There seems to be some communication trouble.

Please try this and see if it is any closer to your desired results.

SELECT
[FileName],
[Trade Name],
[Invoice Number],
[Invoice Date],
(SELECT count(*) FROM PlacedOrderDetails O WHERE P.[FileName] = O.[FileName]) as [FileCount]                      
FROM  PlacedOrderDetails P
WHERE  CreatedDate >= '12/21/2012'

Thank you for helping.

Sounds simple, but it is complicated.

I have attached the spreadsheet with sample data and expected output.

Hope this will help me as well as experts can bring new query logic !!
ExpectedOutput.xls

I omitted the CreatedDate since your example did not show it and none of the invoice dates were greater than or equal to 12/21/2012, but it can easily be included in the common table expression.

I am sure my code works. inside the CTE, I have 2 functions with ROW_NUMBER(), one with ORDER BY invoicedate ASC, and one with DESC ...
rn = 1 to return the one with FILE_COUNT = "max" ...