Problem with dublicates and SUM Sql Query

I have 2 tables:

Customer table:
customer(nvarchar(255))

Certificates
customer(nvarchar(255))
cert(int)


Customer

570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266
570715000000038266

Certificate
    Customer                     cert
570715000000038266      1383
570715000000038266      1656
570715000000038266      1944
570715000000038266      -1383
570715000000038266      -1350
570715000000038266      1350
570715000000038266      -1944
570715000000038266      850
570715000000038266      -1532
570715000000038266      1532
570715000000038266      774
570715000000038266      -1656
570715000000038266      -774


When I execute this query:

SELECT     [Customer].[Customer], SUM(Certificate.Cert)
FROM         [Customer]
inner JOIN Certificate ON [Customer].[Customer] = Certificate.[Customer]
WHERE [Customer].[Customer] = '570715000000038266'
GROUP BY [Customer].[Customer]

I get this result:
 Customer                           Cert
570715000000038266    12750

It multiplies the customer records with all the certificates lines.
15 customers records X all the matching cert records = 12750

The result i am looking for is:

 Customer                           Cert
570715000000038266    850    (12750/15=850)

There are more than one customer in the customer table with multiple lines…


Hope you can help!?
MadsingAsked:
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dwe761Connect With a Mentor Software EngineerCommented:
Madsing,
It might help us to know what question you are actually trying to answer with your query?

I'm not sure where you got 12750 unless it is the absolute value of all of the certs.  From the data you've shown us, the 850 you want is actually the only cert that does not have a matching negative cert.

So if you just want to find the sum of certs for a single Customer, it seems you'd want something like this:


SELECT     c.[Customer], SUM(Certificate.Cert)
FROM      ( SELECT DISTINCT Customer FROM [Customer]) c
inner JOIN Certificate ON c.[Customer] = Certificate.[Customer]
WHERE c.[Customer] = '570715000000038266'
GROUP BY c.[Customer]

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pivarCommented:
Hi,

Try


SELECT     [Customer].[Customer], SUM(Certificate.Cert), AVG(Certificate.Cert)
FROM         [Customer]
inner JOIN Certificate ON [Customer].[Customer] = Certificate.[Customer]
WHERE [Customer].[Customer] = '570715000000038266'
GROUP BY [Customer].[Customer]

/peter
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MadsingAuthor Commented:
Then I get:

Customer                          (Cert)             (AVG cert)
570715000000038266      12750      65,3846153846154

So that is no good.
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DavidMorrisonCommented:
I think what you need is:

SELECT     [Customer].[Customer],
sum(Certificate.Cert) over (partition by [Customer].[Customer]) /
count(*) over (partition by [Customer].[Customer]) as Cert
FROM         [Customer]
inner JOIN Certificate ON [Customer].[Customer] = Certificate.[Customer]
WHERE [Customer].[Customer] = '570715000000038266'
GROUP BY [Customer].[Customer]
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pivarCommented:
How about


SELECT     [Customer].[Customer], SUM(Certificates.Cert),
SUM(Certificates.Cert)/(SELECT COUNT(Customer) FROM Customer x WHERE x.Customer  = [Customer].[Customer])
FROM         [Customer]
inner JOIN Certificates ON [Customer].[Customer] = Certificates.[Customer]
WHERE [Customer].[Customer] = '570715000000038266'
GROUP BY [Customer].[Customer]
0
 
pivarCommented:
Or why not


SELECT     [Customer], SUM(Certificates.Cert)
FROM Certificates
WHERE [Customer] = '570715000000038266'
GROUP BY [Customer]
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DavidMorrisonCommented:
Pivar, I hate to be critical of another professional but are you even reading what OP has asked for?


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pivarCommented:
Please be critical, but please also be clear of what you referring to. I may have misunderstood the question. But right now I don't understand what you getting at.  
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dwe761Software EngineerCommented:
Oh, I see where you got 12750.  Since you have 15 rows in your Customer table and only one row in your Certs table that does not have a matching negative cert, your query found those 15 matches on 850 and you asked it to sum them which it gave you 12750.  All other rows cancelled themselves out because they all had matching positive and negative numbers on the same cert.

So even though my query will give you what you want for a single customer, I'm still not sure that's what your original intent was.  If you remove the WHERE clause on my query, you'll just get the sum of all positive certs without matching negative certs which may be kind of meaningless.  You'll have to answer that.  Are you looking for all customer's certs that do not have a matching negative cert?

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