TIPS-SELECT DISTINCT IN ADO.NET

static void testDistinct()

{

    DataTable t = new DataTable();

    t.Columns.Add("Category", typeof(string));

    t.Columns.Add("Product", typeof(string));

    t.Columns.Add("Version", typeof(string));

    t.Rows.Add("OS", "Windows", "2003");

    t.Rows.Add("OS", "Windows", "Vista");

    t.Rows.Add("Application", "Office", "XP");

    t.Rows.Add("Application", "Office", "2003");

    t.Rows.Add("Application", "Project", "2003");

    t.Rows.Add("Database", "SQL", "2000");

    t.Rows.Add("Database", "SQL", "2005");

    t.Rows.Add("Database", "SQL", "2000"); //Duplicated

    Console.WriteLine("Original Rows Count = "

        + t.Rows.Count.ToString());

    Console.WriteLine("DISTINCT Category Rows Count = " + t.DefaultView

        .ToTable(true, "Category").Rows.Count.ToString());

    Console.WriteLine("DISTINCT Category, Product Rows Count = " + t.DefaultView

        .ToTable(true, "Category", "Product").Rows.Count.ToString());

    Console.WriteLine("DISTINCT Category, Product, Version Rows Count = " + t.DefaultView

        .ToTable(true, "Category", "Product", "Version").Rows.Count.ToString());

}

//...省略...

    t.Rows.Add("Database", "SQL", "2005");

    t.Rows.Add("Database", "SQL", "2000"); //Duplicated

    var rows = from row in t.AsEnumerable()

               select new

               {

                   Category = row.Field<string>("Category"),

                   Product = row.Field<string>("Product")

               };

    Console.WriteLine("Orig RowCount=" + (rows).Count());

    Console.WriteLine("Distinct RowCount=" + (rows).Distinct().Count());