Using a Pivot() operator in SQL Server

Pivot() is a relational operator that changes a table-valued expression into another table. It rotates the table-valued expression by turning the unique values from one column  in the expression into multiple columns in the output and performs aggregations where they are required on any remaining column values that are wanted in the final output.

This is the syntax from MSDN for the PIVOT operator.

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SELECT , 
    [first pivoted column] AS , 
    [second pivoted column] AS , 
    ... 
    [last pivoted column] AS  
FROM 
    ()       AS   PIVOT  (      ()  FOR   []       IN ( [first pivoted column], [second pivoted column],      ... [last pivoted column])  ) AS   ;

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Let us take an example frrom Northwind database. Here is a query that Selects lastname of employee and Unitprice from the Order Details table for UnitPrice greater than 50 and Quantity>10.

Pivot_0.png

You can see that Employees figure in many orders (have order details) with different UnitPrices. Now if you want to aggreegate the average Unitprice of articles sold by each employee (or a chosen number of employees) you need to do an aggregate.

For the above query we cannot directly use the PIVOT operator and we need to create an ALIAS as shown. PriceTable is the ALIAS for this query

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Select * FROM
(SELECT        Employees.LastName, [Order Details].UnitPrice
FROM            Employees INNER JOIN
                         Orders ON Employees.EmployeeID = Orders.EmployeeID INNER JOIN
                         [Order Details] ON Orders.OrderID = [Order Details].OrderID INNER JOIN
                         Products ON [Order Details].ProductID = Products.ProductID
WHERE [Order Details].UnitPrice >50.00 and [Order Details].Quantity>10)
as PriceTable

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Nothing is changed as far as the Query return is concerned but we now have an  ALIAS.

Now we create a table which aggregates the average of UnitPrice for some named Employees using their LastName from the PriceTable as shown here.

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Select * FROM
(SELECT        Employees.LastName, [Order Details].UnitPrice
FROM            Employees INNER JOIN
                         Orders ON Employees.EmployeeID = Orders.EmployeeID INNER JOIN
                         [Order Details] ON Orders.OrderID = [Order Details].OrderID INNER JOIN
                         Products ON [Order Details].ProductID = Products.ProductID
WHERE [Order Details].UnitPrice >50.00 and [Order Details].Quantity>10)
as PriceTable
Pivot(Avg(UnitPrice) For LastName in ([King], [Davolio], [Fuller],[Peacock],[Suyama]))
as StudentPivot

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When you run this the response is a table that has the values we were looking for: