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Creating Functions, Stored Procedures, and Triggers in VS .NET
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Each function must have a unique name that conforms to the rules for object identifiers. Although you do not have to define input parameters for functions, it is rare for UDFs to not have input parameters. So you will usually specify one or more input parameters along with the data type of each parameter. You use the statement s RETURNS clause to specify the data type of the scalar value that the function will return. There are several options that you can specify for this clause. When you specify ENCRYPTION, SQL Server encrypts the definition of the function when it is stored. The SCHEMABINDING option prevents any objects that the function depends on from being dropped. The EXECUTE AS option specifies the security context of the function. The body of the function is delimited by a BEGIN END construct, which must include a RETURN clause that is used to output the value that the function calculates. The body of the function is obviously where all the interesting work happens. Although you can execute virtually any valid batch of code within a function, functions do have some restrictions. The most significant restriction is that you cannot use a function to change the state of any object in a database or the database itself. Therefore, you cannot insert, update, or delete data in tables, nor can you create, alter, or drop objects in the database. However, you can create one or more table variables and issue INSERT, UPDATE, and DELETE statements against the table variable. MORE INFO
Table variables
A table variable is a special type of variable used to temporarily store a set of rows that will be returned as the result of a table-valued function. For information about table variables, see the SQL Server 2005 Books Online topic Table (Transact-SQL). Because scalar functions return a single value, you normally use them in the column list of a SELECT statement and can use them in the WHERE clause as well. The following example shows you how to define a scalar-valued function that returns the stock level for a given product ID: CREATE FUNCTION [dbo].[ufnGetStock](@ProductID [int]) RETURNS [int] AS -- Returns the stock level for the product. This function is used -- internally only. BEGIN DECLARE @ret int;
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