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Using PIVOT and UNPIVOT

You can use the PIVOT and UNPIVOT relational operators to change a table-valued expression into another table. PIVOT rotates a 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. UNPIVOT performs the opposite operation to PIVOT by rotating columns of a table-valued expression into column values.

NoteNote

When PIVOT and UNPIVOT are used against databases that are upgraded to SQL Server 2005 or later, the compatibility level of the database must be set to 90 or higher. For information about how to set the database compatibility level, see sp_dbcmptlevel (Transact-SQL).

The syntax for PIVOT provides is simpler and more readable than the syntax that may otherwise be specified in a complex series of SELECT...CASE statements. For a complete description of the syntax for PIVOT, see FROM (Transact-SQL).

The following is annotated syntax for PIVOT.

SELECT <non-pivoted column>,

    [first pivoted column] AS <column name>,

    [second pivoted column] AS <column name>,

    ...

    [last pivoted column] AS <column name>

FROM

    (<SELECT query that produces the data>)

    AS <alias for the source query>

PIVOT

(

    <aggregation function>(<column being aggregated>)

FOR

[<column that contains the values that will become column headers>]

    IN ( [first pivoted column], [second pivoted column],

    ... [last pivoted column])

) AS <alias for the pivot table>

<optional ORDER BY clause>;

The following code example produces a two-column table that has four rows.

USE AdventureWorks ;
GO
SELECT DaysToManufacture, AVG(StandardCost) AS AverageCost 
FROM Production.Product
GROUP BY DaysToManufacture;

Here is the result set.

DaysToManufacture          AverageCost

0                          5.0885

1                          223.88

2                          359.1082

4                          949.4105

No products are defined with three DaysToManufacture.

The following code displays the same result, pivoted so that the DaysToManufacture values become the column headings. A column is provided for three [3] days, even though the results are NULL.

-- Pivot table with one row and five columns
SELECT 'AverageCost' AS Cost_Sorted_By_Production_Days, 
[0], [1], [2], [3], [4]
FROM
(SELECT DaysToManufacture, StandardCost 
    FROM Production.Product) AS SourceTable
PIVOT
(
AVG(StandardCost)
FOR DaysToManufacture IN ([0], [1], [2], [3], [4])
) AS PivotTable;

Here is the result set.

Cost_Sorted_By_Production_Days    0         1         2           3       4       

AverageCost                       5.0885    223.88    359.1082    NULL    949.4105

A common scenario where PIVOT can be useful is when you want to generate cross-tabulation reports to summarize data. For example, suppose you want to query the PurchaseOrderHeader table in the AdventureWorks sample database to determine the number of purchase orders placed by certain employees. The following query provides this report, ordered by vendor.

USE AdventureWorks;
GO
SELECT VendorID, [164] AS Emp1, [198] AS Emp2, [223] AS Emp3, [231] AS Emp4, [233] AS Emp5
FROM 
(SELECT PurchaseOrderID, EmployeeID, VendorID
FROM Purchasing.PurchaseOrderHeader) p
PIVOT
(
COUNT (PurchaseOrderID)
FOR EmployeeID IN
( [164], [198], [223], [231], [233] )
) AS pvt
ORDER BY pvt.VendorID;

Here is a partial result set.

VendorID    Emp1        Emp2        Emp3        Emp4        Emp5
1           4           3           5           4           4
2           4           1           5           5           5
3           4           3           5           4           4
4           4           2           5           5           4
5           5           1           5           5           5

The results returned by this subselect statement are pivoted on the EmployeeID column.

SELECT PurchaseOrderID, EmployeeID, VendorID
FROM PurchaseOrderHeader;

This means that the unique values returned by the EmployeeID column themselves become fields in the final result set. Therefore, there is a column for each EmployeeID number specified in the pivot clause: in this case employees 164, 198, 223, 231, and 233. The PurchaseOrderID column serves as the value column, against which the columns returned in the final output, which are called the grouping columns, are grouped. In this case, the grouping columns are aggregated by the COUNT function. Notice that a warning message appears that indicates that any null values appearing in the PurchaseOrderID column were not considered when computing the COUNT for each employee.

Important noteImportant

When aggregate functions are used with PIVOT, the presence of any null values in the value column are not considered when computing an aggregation.

UNPIVOT performs almost the reverse operation of PIVOT, by rotating columns into rows. Suppose the table produced in the previous example is stored in the database as pvt, and you want to rotate the column identifiers Emp1, Emp2, Emp3, Emp4, and Emp5 into row values that correspond to a particular vendor. This means that you must identify two additional columns. The column that will contain the column values that you are rotating (Emp1, Emp2,...) will be called Employee, and the column that will hold the values that currently reside under the columns being rotated will be called Orders. These columns correspond to the pivot_column and value_column, respectively, in the Transact-SQL definition. Here is the query.

--Create the table and insert values as portrayed in the previous example.
CREATE TABLE pvt (VendorID int, Emp1 int, Emp2 int,
    Emp3 int, Emp4 int, Emp5 int);
GO
INSERT INTO pvt VALUES (1,4,3,5,4,4);
INSERT INTO pvt VALUES (2,4,1,5,5,5);
INSERT INTO pvt VALUES (3,4,3,5,4,4);
INSERT INTO pvt VALUES (4,4,2,5,5,4);
INSERT INTO pvt VALUES (5,5,1,5,5,5);
GO
--Unpivot the table.
SELECT VendorID, Employee, Orders
FROM 
   (SELECT VendorID, Emp1, Emp2, Emp3, Emp4, Emp5
   FROM pvt) p
UNPIVOT
   (Orders FOR Employee IN 
      (Emp1, Emp2, Emp3, Emp4, Emp5)
)AS unpvt;
GO

Here is a partial result set.

VendorID   Employee   Orders
1      Emp1         4
1      Emp2         3
1      Emp3         5
1      Emp4         4
1      Emp5         4
2      Emp1         4
2      Emp2         1
2      Emp3         5
2      Emp4         5
2      Emp5         5
...

Notice that UNPIVOT is not the exact reverse of PIVOT. PIVOT performs an aggregation and, therefore, merges possible multiple rows into a single row in the output. UNPIVOT does not reproduce the original table-valued expression result because rows have been merged. Besides, null values in the input of UNPIVOT disappear in the output, whereas there may have been original null values in the input before the PIVOT operation.

The Sales.vSalesPersonSalesByFiscalYears view in the AdventureWorks sample database uses PIVOT to return the total sales for each salesperson, for each fiscal year. To script the view in SQL Server Management Studio, in Object Explorer, locate the view under the Views folder for the AdventureWorks database. Right-click the view name, and then select Script View as.

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