Types of Functions
SQL Server 2008 supports user-defined functions and built-in, system, functions.
Scalar 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 AdventureWorks2008R2;
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 a ProductModelID between 75 and 80.
USE AdventureWorks2008R2;
GO
SELECT ProductModelID, Name, dbo.ufnGetInventoryStock(ProductID)AS CurrentSupply
FROM Production.Product
WHERE ProductModelID BETWEEN 75 and 80;
GO
Table-Valued Functions
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 AdventureWorks2008R2;
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 '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
JOIN Sales.Customer AS C ON SH.CustomerID = C.CustomerID
WHERE C.StoreID = @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 AdventureWorks2008R2;
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,
FirstName nvarchar(255) NOT NULL,
LastName nvarchar(255) NOT NULL,
JobTitle nvarchar(50) NOT NULL,
RecursionLevel int NOT NULL
)
--Returns a result set that lists all the employees who report to the
--specific employee directly or indirectly.*/
AS
BEGIN
WITH EMP_cte(EmployeeID, OrganizationNode, FirstName, LastName, JobTitle, RecursionLevel) -- CTE name and columns
AS (
SELECT e.BusinessEntityID, e.OrganizationNode, p.FirstName, p.LastName, e.JobTitle, 0 -- Get the initial list of Employees for Manager n
FROM HumanResources.Employee e
INNER JOIN Person.Person p
ON p.BusinessEntityID = e.BusinessEntityID
WHERE e.BusinessEntityID = @InEmpID
UNION ALL
SELECT e.BusinessEntityID, e.OrganizationNode, p.FirstName, p.LastName, e.JobTitle, RecursionLevel + 1 -- Join recursive member to anchor
FROM HumanResources.Employee e
INNER JOIN EMP_cte
ON e.OrganizationNode.GetAncestor(1) = EMP_cte.OrganizationNode
INNER JOIN Person.Person p
ON p.BusinessEntityID = e.BusinessEntityID
)
-- copy the required columns to the result of the function
INSERT @retFindReports
SELECT EmployeeID, FirstName, LastName, JobTitle, RecursionLevel
FROM EMP_cte
RETURN
END;
GO
-- Example invocation
SELECT EmployeeID, FirstName, LastName, JobTitle, RecursionLevel
FROM dbo.ufn_FindReports(1);
GO
Built-in Functions
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 Built-in 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.