1. Module 9: Implementing Functions

2. Overview Creating and Using Functions Working with Functions Controlling Execution Context

3. Lesson 1: Creating and Using Functions Types of Functions What Is a Scalar Function? What Is an Inline Table-Valued Function? What Is a Multi-Statement Table-Valued Function? Practice: Creating Functions

4. Types of Functions Scalar functions  Similar to built-in functions  Return a single value Inline table-valued functions  Similar to views with parameters  Return a table as the result of single SELECT statement Multi-statement table-valued functions  Similar to stored procedures  Return a new table as the result of INSERT statements

5. What Is a Scalar Function? RETURNS clause specifies data type Function is defined within a BEGIN…END block Can be invoked anywhere a scalar expression of the same data type is allowed CREATE FUNCTION Sales.SumSold(@ProductID int) RETURNS int AS BEGIN DECLARE @ret int SELECT @ret = SUM(OrderQty) FROM Sales.SalesOrderDetail WHERE ProductID = @ProductID IF (@ret IS NULL) SET @ret = 0 RETURN @ret END CREATE FUNCTION Sales.SumSold(@ProductID int) RETURNS int AS BEGIN DECLARE @ret int SELECT @ret = SUM(OrderQty) FROM Sales.SalesOrderDetail WHERE ProductID = @ProductID IF (@ret IS NULL) SET @ret = 0 RETURN @ret END SELECT ProductID, Name, Sales.SumSold(ProductID) AS SumSold FROM Production.Product SELECT ProductID, Name, Sales.SumSold(ProductID) AS SumSold FROM Production.Product

6. What Is an Inline Table-Valued Function? RETURNS specifies table as data type Format is defined by result set Content of function is a SELECT statement CREATE FUNCTION HumanResources.EmployeesForManager (@ManagerId int) RETURNS TABLE AS RETURN ( SELECTFirstName, LastName FROM HumanResources.Employee Employee INNER JOIN Person.Contact Contact ON Employee.ContactID = Contact.ContactID WHERE ManagerID = @ManagerId ) CREATE FUNCTION HumanResources.EmployeesForManager (@ManagerId int) RETURNS TABLE AS RETURN ( SELECTFirstName, LastName FROM HumanResources.Employee Employee INNER JOIN Person.Contact Contact ON Employee.ContactID = Contact.ContactID WHERE ManagerID = @ManagerId ) SELECT * FROM HumanResources.EmployeesForManager(3) -- OR SELECT * FROM HumanResources.EmployeesForManager(6) SELECT * FROM HumanResources.EmployeesForManager(3) -- OR SELECT * FROM HumanResources.EmployeesForManager(6)

7. What Is a Multi-Statement Table-Valued Function? RETURNS specifies table data type and defines structure BEGIN and END enclose multiple statements CREATE FUNCTION HumanResources.EmployeeNames (@format nvarchar(9)) RETURNS @tbl_Employees TABLE (EmployeeID int PRIMARY KEY, [Employee Name] nvarchar(100)) AS BEGIN IF (@format = 'SHORTNAME') INSERT @tbl_Employees SELECT EmployeeID, LastName FROM HumanResources.vEmployee ELSE IF (@format = 'LONGNAME') INSERT @tbl_Employees SELECT EmployeeID, (FirstName + ' ' + LastName) FROM HumanResources.vEmployee RETURN END CREATE FUNCTION HumanResources.EmployeeNames (@format nvarchar(9)) RETURNS @tbl_Employees TABLE (EmployeeID int PRIMARY KEY, [Employee Name] nvarchar(100)) AS BEGIN IF (@format = 'SHORTNAME') INSERT @tbl_Employees SELECT EmployeeID, LastName FROM HumanResources.vEmployee ELSE IF (@format = 'LONGNAME') INSERT @tbl_Employees SELECT EmployeeID, (FirstName + ' ' + LastName) FROM HumanResources.vEmployee RETURN END SELECT * FROM HumanResources.EmployeeNames('LONGNAME')

8. Practice: Creating Functions In this practice, you will: Create a scalar function Create an inline table-valued function Create a multi-statement table-valued function Drop user-defined functions

9. Lesson 2: Working with Functions Guidelines for Creating Functions Rewriting Stored Procedures as Functions Deterministic and Nondeterministic Functions

10. Deterministic functions  Always returns the same value for the same set of input values and database state  Results can be indexed  Aggregate and string built-in functions Nondeterministic functions  May return different results for the same set of input values and database state  Results cannot be indexed  Configuration, cursor, metadata, security, system statistics built-in functions

11. Guidelines for Creating Functions Determine function type Create one function for one task Create, test, and troubleshoot Qualify object names inside function Consider ability of SQL Server 2005 to index function results

12. Rewriting Stored Procedures as Functions Table-valued functions Single SELECT statement with parameters No update operations No need for dynamic EXECUTE statements Build intermediate results in to a temporary table Single SELECT statement with parameters No update operations No need for dynamic EXECUTE statements Build intermediate results in to a temporary table Converting stored procedures to functions For single resultset use a table-valued function For single scalar value use a scalar function For single resultset use a table-valued function For single scalar value use a scalar function

13. Lesson 3: Controlling Execution Context What Is Execution Context? The EXECUTE AS Clause Options for Extending Impersonation Context Demonstration: Controlling Execution Context

14. What Is Execution Context? Sales.Order (Owner: John) Sales.Order (Owner: John) Ted (No permissions) Ted (No permissions) Function (Owner: Pat) Function (Owner: Pat) GetOrders Ted (EXECUTE permission) Ted (EXECUTE permission) Pat (SELECT permission) Pat (SELECT permission) CREATE FUNCTION GetOrders RETURNS TABLE AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS 'Pat' AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS 'Pat' AS RETURN ( SELECT * FROM Sales.Order )

15. EXECUTE AS options The EXECUTE AS Clause The caller of the module The person creating or altering the module The owner of the module A specified user CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS CALLER AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS CALLER AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS SELF AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS SELF AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS OWNER AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS OWNER AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS 'Pat' AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS 'Pat' AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS { CALLER | SELF | OWNER | user_name } AS RETURN ( SELECT * FROM Sales.Order ) CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS { CALLER | SELF | OWNER | user_name } AS RETURN ( SELECT * FROM Sales.Order )

16. Options for Extending Impersonation Context EXECUTE AS is restricted to current database by default Establish a trust relationship to extend impersonation to other databases dbo Mapped dbo Signed Code Module Certificate User GRANT AUTHENTICATE … SET TRUSTWORTHY ON

17. Demonstration: Controlling Execution Context In this demonstration, you will see how to use execution context within a stored procedure

18. Lab: Implementing Functions Exercise 1: Creating Functions Exercise 2: Controlling Execution Context