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Types of Functions

SQL Server 2005 supports user-defined functions and built-in, system, functions.

User-defined scalar functions return a single data value of the type defined in the RETURNS clause. For an inline scalar function, there is no function body; the scalar value is the result of a single statement. For a multistatement scalar function, the function body, defined in a BEGIN...END block, contains a series of Transact-SQL statements that return the single value. The return type can be any data type except text, ntext, image, cursor, and timestamp.

The following examples creates a multistatement scalar function. The function takes one input value, a ProductID, and returns a single data value, the aggregated quantity of the specified product in inventory.

USE AdventureWorks;
GO
IF OBJECT_ID (N'dbo.ufnGetInventoryStock', N'FN') IS NOT NULL
    DROP FUNCTION ufnGetInventoryStock;
GO
CREATE FUNCTION dbo.ufnGetInventoryStock(@ProductID int)
RETURNS int 
AS 
-- Returns the stock level for the product.
BEGIN
    DECLARE @ret int;
    SELECT @ret = SUM(p.Quantity) 
    FROM Production.ProductInventory p 
    WHERE p.ProductID = @ProductID 
        AND p.LocationID = '6';
     IF (@ret IS NULL) 
        SET @ret = 0;
    RETURN @ret;
END;
GO

The following example uses the ufnGetInventoryStock function to return the current inventory quantity for products that have an ProductModelID between 75 and 80.

USE AdventureWorks;
GO
SELECT ProductModelID, Name, dbo.ufnGetInventoryStock(ProductID)AS CurrentSupply
FROM Production.Product
WHERE ProductModelID BETWEEN 75 and 80;
GO

User-defined table-valued functions return a table data type. For an inline table-valued function, there is no function body; the table is the result set of a single SELECT statement.

The following example creates an inline table-valued function. The function takes one input parameter, a customer (store) ID, and returns the columns ProductID, Name, and the aggregate of year-to-date sales as YTD Total for each product sold to the store.

USE AdventureWorks;
GO
IF OBJECT_ID (N'Sales.ufn_SalesByStore', N'IF') IS NOT NULL
    DROP FUNCTION Sales.ufn_SalesByStore;
GO
CREATE FUNCTION Sales.ufn_SalesByStore (@storeid int)
RETURNS TABLE
AS
RETURN 
(
    SELECT P.ProductID, P.Name, SUM(SD.LineTotal) AS 'YTD Total'
    FROM Production.Product AS P 
      JOIN Sales.SalesOrderDetail AS SD ON SD.ProductID = P.ProductID
      JOIN Sales.SalesOrderHeader AS SH ON SH.SalesOrderID = SD.SalesOrderID
    WHERE SH.CustomerID = @storeid
    GROUP BY P.ProductID, P.Name
);
GO

The following example invokes the function and specifies customer ID 602.

SELECT * FROM Sales.ufn_SalesByStore (602);

For a multistatement table-valued function, the function body, defined in a BEGIN...END block, contains a series of Transact-SQL statements that build and insert rows into the table that will be returned.

The following example creates a table-valued function. The function takes a single input parameter, an EmployeeID and returns a list of all the employees who report to the specified employee directly or indirectly. The function is then invoked specifying employee ID 109.

USE AdventureWorks;
GO
IF OBJECT_ID (N'dbo.ufn_FindReports', N'TF') IS NOT NULL
    DROP FUNCTION dbo.ufn_FindReports;
GO
CREATE FUNCTION dbo.ufn_FindReports (@InEmpID INTEGER)
RETURNS @retFindReports TABLE 
(
    EmployeeID int primary key NOT NULL,
    Name nvarchar(255) NOT NULL,
    Title nvarchar(50) NOT NULL,
    EmployeeLevel int NOT NULL,
    Sort nvarchar (255) NOT NULL
)
--Returns a result set that lists all the employees who report to the 
--specific employee directly or indirectly.*/
AS
BEGIN
   WITH DirectReports(Name, Title, EmployeeID, EmployeeLevel, Sort) AS
    (SELECT CONVERT(Varchar(255), c.FirstName + ' ' + c.LastName),
        e.Title,
        e.EmployeeID,
        1,
        CONVERT(Varchar(255), c.FirstName + ' ' + c.LastName)
     FROM HumanResources.Employee AS e
          JOIN Person.Contact AS c ON e.ContactID = c.ContactID 
     WHERE e.EmployeeID = @InEmpID
   UNION ALL
     SELECT CONVERT(Varchar(255), REPLICATE ('| ' , EmployeeLevel) +
        c.FirstName + ' ' + c.LastName),
        e.Title,
        e.EmployeeID,
        EmployeeLevel + 1,
        CONVERT (Varchar(255), RTRIM(Sort) + '| ' + FirstName + ' ' + 
                 LastName)
     FROM HumanResources.Employee as e
          JOIN Person.Contact AS c ON e.ContactID = c.ContactID
          JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID
    )
-- copy the required columns to the result of the function 
   INSERT @retFindReports
   SELECT EmployeeID, Name, Title, EmployeeLevel, Sort
   FROM DirectReports 
   RETURN
END;
GO
-- Example invocation
SELECT EmployeeID, Name, Title, EmployeeLevel
FROM dbo.ufn_FindReports(109)
ORDER BY Sort;
GO

Built-in functions are provided by SQL Server to help you perform a variety of operations. They cannot be modified. You can use built-in functions in Transact-SQL statements to:

  • Access information from SQL Server system tables without accessing the system tables directly. For more information, see Using System Functions.
  • Perform common tasks such as SUM, GETDATE, or IDENTITY. For more information, see Functions (Transact-SQL).

Built-in functions return either scalar or table data types. For example, @@ERROR returns 0 if the last Transact-SQL statement executed successfully. If the statement generated an error, @@ERROR returns the error number. And the function SUM(parameter) returns the sum of all the values for the parameter.

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