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SQL Server Query Help

Posted on 2011-02-16
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Last Modified: 2012-08-13
Hi Experts,

I have a customersales table and I am using the below query to find out the maximum salesid for each customer.

SELECT MAX(SaleID),CustomerID
FROM CustomerSales
GROUP BY CustomerID

It takes a very high cpu and time. CustomerSales table has 4 million records.

Can you please guide me if there a better and efficient way to write this query.

Thanks,
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Question by:rocky_lotus_newbie
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7 Comments
 
LVL 32

Accepted Solution

by:
Ephraim Wangoya earned 500 total points
ID: 34910778
Do you have SaleID and CustomerID fileds indexed
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LVL 58

Assisted Solution

by:cyberkiwi
cyberkiwi earned 1000 total points
ID: 34910781
The query is as good as it gets.
However, you will find it runs MUCH faster, if you add an index on customerid, saleid

e.g.

create index ix_customersales_cs on CustomerSales (customerid, saleid)
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LVL 58

Assisted Solution

by:cyberkiwi
cyberkiwi earned 1000 total points
ID: 34910784
Not separately, mind you, but one index involving both fields.
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LVL 1

Assisted Solution

by:spmamidi
spmamidi earned 500 total points
ID: 34910862


I hope you would be having Clustered Index if not there use the following query

CREATE UNIQUE CLUSTERED INDEX Sales_ID_Index ON CustomerSales (CustomerSalesID);
GO

Next, build three similar nonclustered indexes:
-- The first index is on a single, nonunique column
CREATE INDEX SalesOrderID_Index1 ON CustomerSales(SaleID);
GO
-- The second index is composite and explicitly adds the clustered key column
CREATE  INDEX SalesOrderID_Index2 ON CustomerSales(SaleID, CustomerID);
GO
-- The third index adds the clustered index key as an INCLUDE column
CREATE  INDEX Sales_DetailID_Index3 ON CustomerSales(SaleID);
      INCLUDE (CustomerID);
GO

Hopefully you would get good performance results.

Shiva Mamidi



Shiva Mamidi
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LVL 4

Author Comment

by:rocky_lotus_newbie
ID: 34912061
Thanks for the Inputs, I will try these indexes and see if it performs better.
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LVL 58

Expert Comment

by:cyberkiwi
ID: 34912892
Shiva - you want to create 3 indexes ALL on the same [first] column on a SINGLE table??
0
 
LVL 1

Expert Comment

by:spmamidi
ID: 34916172

Yes - There is a typo for Creating third Index.

Here is the correct version - CREATE  INDEX Sales_OrderId_Index3 ON CustomerSales(SaleID) INCLUDE (CustomerID);

Shiva Mamidi
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