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.