Tài liệu Executing SQL Server User-Defined Scalar Functions doc

[ Team LiB ]Recipe 2.13 Executing SQL Server User-Defined Scalar Functions Problem Your SQL Server 2000 database includes a user-defined function that returns a scalar value.. You want

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Recipe 2.13 Executing SQL Server User-Defined Scalar Functions

Problem

Your SQL Server 2000 database includes a user-defined function that returns a scalar value You want to retrieve the value from this function using ADO.NET

Solution

Invoke the function as you would a query or stored procedure

The sample code, as shown in Example 2-16, uses a single SQL Server function:

ExtendedPrice

Calculates and returns the extended price for an order line item based on the unit price, quantity, and discount

Example 2-16 SQL Server function: ExtendedPrice

CREATE FUNCTION dbo.ExtendedPrice

(

@UnitPrice money,

@Quantity smallint,

@Discount real

)

RETURNS money

AS

BEGIN

RETURN ((@UnitPrice * @Quantity) * (1 - @Discount))

END

The sample code defines a SQL statement that uses the ExtendedPrice user-defined

function The statement is used by a DataAdapter to fill a DataTable with all records from the Order Details table in Northwind together with the extended price calculation for each record The default view of the table is bound to a data grid on the form

The C# code is shown in Example 2-17

Example 2-17 File: ScalarFunctionForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Data;

using System.Data.SqlClient;

//

String sqlText = "SELECT *, " +

"dbo.ExtendedPrice(UnitPrice, Quantity, Discount) ExtendedPrice " +

"FROM [Order Details]";

// Create DataAdapter and fill the table

SqlDataAdapter da = new SqlDataAdapter(sqlText,

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable dt = new DataTable( );

da.Fill(dt);

// Bind the default view for the table to the grid

resultDataGrid.DataSource = dt;

Discussion

A user-defined scalar function is a SQL routine that accepts one or more scalar input parameters and returns a single value A user-defined scalar function is invoked from a query or executed like a stored procedure using an EXECUTE statement

You can invoke scalar functions where scalar expressions can be used To invoke a scalar function, use the following syntax:

[databaseName.]ownerName.functionName([argument1][, ])

In the solution code, the ExtendedPrice function is called as shown by:

dbo.ExtendedPrice(UnitPrice, Quantity, Discount)

This calculates the extended price for each row in the Order Details table based on the UnitPrice, Quantity, and Discount values The result is returned as a result set column named ExtendedPrice

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