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Module 8: Implementing Functions

Module 8: Implementing Functions. Module 8:Implementing Functions. Introducing Functions Working with Functions Controlling Execution Context. Lesson 1: Introducing Functions. Types of Functions What Is a Scalar Function? What Is an Inline Table-Valued Function?

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Module 8: Implementing Functions

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  1. Module 8:Implementing Functions

  2. Module 8:Implementing Functions • Introducing Functions • Working with Functions • Controlling Execution Context

  3. Lesson 1: Introducing Functions • Types of Functions • What Is a Scalar Function? • What Is an Inline Table-Valued Function? • What Is a Multi-Statement Table-Valued Function?

  4. Types of Functions Types of Functions Scalar Functions ü Inline Table-Valued Functions ü Multi-Statement Table-Valued Functions ü Built-in Functions ü

  5. What Is a Scalar Function? Scalar Functions: Return a single data value ü Can be either inline or multi-statement ü Can return any data type except for text, ntext, image, cursor, and timestamps ü CREATE FUNCTION [ schema_name. ] function_name ( [ { @parameter_name [ AS ][ type_schema_name. ] parameter_data_type [ = default ] [ READONLY ] } [ ,...n ] ] ) RETURNS return_data_type

  6. What Is an Inline Table-Valued Function? Inline Table-Valued Function: Returns a TABLE data-type ü Has no function body ü Is comprised of a single result set ü CREATE FUNCTION [ schema_name. ] function_name ( [ { @parameter_name [ AS ] [ type_schema_name. ] parameter_data_type [ = default ] [ READONLY ] } [ ,...n ] ] ) RETURNS TABLE

  7. What Is a Multi-Statement Table-Valued Function? Multi-statement Table-Valued Function: Returns a TABLE data-type ü Has a function body defined by BEGIN and END blocks ü Defines a table-type variable and schema ü Inserts rows from multiple Transact-SQL statements into the returned table ü CREATE FUNCTION [ schema_name. ] function_name ( [ { @parameter_name [ AS ] [ type_schema_name. ] parameter_data_type [ = default ] [READONLY] } [ ,...n ] ] ) RETURNS @return_variable TABLE <table_type_definition>

  8. Demonstration: Creating Functions • In this demonstration, you will see how to: • How to create an inline scalar function • Call your function from a Transact-SQL statement

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

  10. Deterministic and Nondeterministic Functions Determines whether a user defined function is deterministic or not SELECT [IsDeterministic] = objectproperty(object_id('dbo.myUDF'), 'IsDeterministic')

  11. Guidelines for Creating Functions Determine function type ü Create one function for one task ü Create, test, and troubleshoot ü Qualify object names inside function ü Consider ability of SQL Server 2008 to index function results ü

  12. Rewriting Stored Procedures as Functions Convert your stored procedure to a function if: It is expressible as a single SELECT statement ü It does not perform update operations ü It does not require a dynamic EXECUTE statement ü It only returns one result set ü Its primary purpose is to build intermediate results ü

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

  14. What Is Execution Context? Ted (No permissions) Pat (SELECT permission) Sales.Order (Owner: John) GetOrders Ted (EXECUTE permission) Function (Owner: Pat) Pat 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 )

  15. The EXECUTE AS Clause The Execute AS Clause: Enables Impersonation ü Provides access to modules via impersonation ü Can be used to impersonate server-level principals or logins via the EXECUTE AS LOGIN statement ü Can be used to impersonate database level principals or users via the EXECUTE AS USER statement ü CREATE FUNCTION GetOrders RETURNS TABLE WITH EXECUTE AS { CALLER | SELF | OWNER | ‘user_name’ } AS RETURN ( SELECT * FROM Sales.Order )

  16. Extending Impersonation Context Required conditions for extending impersonation scope: Authenticator must be trusted in target scope ü Source database must be marked as trustworthy ü

  17. Lab: Implementing Functions • Exercise 1: Creating Functions • Exercise 2: Controlling Execution Context Logon information Estimated time: 60 minutes

  18. Lab Scenario Adventure Works maintains a list of special offers and discounts for various products throughout the year that applies to both customers and resellers. Currently, this information is only accessible directly from the Sales.SpecialOffer table. A new requirement is to retrieve this information by using user-defined functions. For this, you need to create a scalar user-defined function named GetCurrencyRate within the Sales schema that retrieves the latest currency conversion rate for a specific currency. You must then establish a trust relationship between the AdventureWorks2008 and AdventureWorksDW2008 databases to enable the GetCurrencyRate function to retrieve the currency data. Finally, you need to create a multi-statement table-valued user-defined function named GetCurrencyDiscountedProducts within the Sales schema that that uses a complex query to retrieve products that have a discount.

  19. Lab Review • When might it be practical to use an Inline Table-Valued Function? • When would you use the Authenticate permission?

  20. Module Review and Takeaways Review Questions Real-world Issues and Scenarios

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