Use a relationship with a calculated column : DataColumn « ADO.Net « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. ADO.Net
3. DataColumn

using System;
using System.Data;
using System.Data.SqlClient;

public class CalculatedColumn
{
    public static void Main() 
    {
        string connectionString = "Data Source=localhost;Initial Catalog=Northwind;Integrated Security=SSPI";
        string SQL = "SELECT * FROM Categories";

        SqlConnection con = new SqlConnection(connectionString);
        SqlCommand cmd = new SqlCommand(SQL, con);
        SqlDataAdapter adapter = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();

        con.Open();
        adapter.Fill(ds, "Categories");
    
        cmd.CommandText = "SELECT * FROM Products";
        adapter.Fill(ds, "Products");
        con.Close();
        DataColumn parentCol = ds.Tables["Categories"].Columns["CategoryID"];
        DataColumn childCol = ds.Tables["Products"].Columns["CategoryID"];
        DataRelation relation = new DataRelation("Cat_Prod", parentCol,childCol);
        ds.Relations.Add(relation);

        ds.Tables["Categories"].Columns.Add("AveragePrice", typeof(Decimal), "AVG(Child(Cat_Prod).UnitPrice)");
        ds.Tables["Categories"].Columns.Add("TotalPrice", typeof(Decimal), "SUM(Child(Cat_Prod).UnitPrice)");

        foreach (DataRow row in ds.Tables["Categories"].Rows)
        {
            Console.WriteLine(row["CategoryName"]);
            Console.WriteLine(row["AveragePrice"]);
            Console.WriteLine(row["TotalPrice"]);
        }
    }
}