Question

While running the code it is giving error ” Cannot find column [max].” but i have added the max and min column to the table in the dataset

MySql.Data.MySqlClient.MySqlConnection mycon = new MySqlConnection(GetConnectionString());
    if (mycon.State != ConnectionState.Open)

        {

            string sqlCat = "SELECT * FROM out_of_mark_table";
            string sqlProd = "SELECT * FROM scord_mark_table";

            MySqlDataAdapter da = new MySqlDataAdapter(sqlCat, mycon);
            DataSet ds = new DataSet();

            try
            {
                mycon.Open();
                da.Fill(ds, "out_of_mark_table");

                da.SelectCommand.CommandText = sqlProd;
                da.Fill(ds, "scord_mark_table");
            }
            finally
            {
                mycon.Close();
            }

            DataRelation relat = new DataRelation("CatProds", ds.Tables["out_of_mark_table"].Columns["test_id"], ds.Tables["scord_mark_table"].Columns["test_id"]);
            ds.Relations.Add(relat);

            DataColumn count = new DataColumn("Products (#)", typeof(int), "COUNT(Child(CatProds).test_id)");
            DataColumn max = new DataColumn("Most Expensive Product", typeof(decimal), "MAX(Child(CatProds).total)");
            DataColumn min = new DataColumn("Least Expensive Product", typeof(decimal), "MIN(Child(CatProds).total)");
            DataColumn no=new DataColumn("No");
            DataColumn IdCol = new DataColumn();
            min.Caption = "min";
            max.Caption = "max";
            string expr = "max * min";

            IdCol.ColumnName = "ID";
            IdCol.DataType = Type.GetType("System.Int32");
            IdCol.ReadOnly = true;
            IdCol.AllowDBNull = false;
            //IdCol.Unique = true;
            IdCol.AutoIncrement = true;
            IdCol.AutoIncrementSeed = 1;
            IdCol.AutoIncrementStep = 1;



            ds.Tables["out_of_mark_table"].Columns.Add(count);
            ds.Tables["out_of_mark_table"].Columns.Add(max);
            ds.Tables["out_of_mark_table"].Columns.Add(min);
            ds.Tables["out_of_mark_table"].Columns.Add(IdCol);
            DataColumn sum = new DataColumn("Sum of", typeof(int), expr, MappingType.Attribute);
            **ds.Tables["out_of_mark_table"].Columns.Add(sum);**
            IdCol.SetOrdinal(0);
            GridView1.DataSource = ds.Tables["out_of_mark_table"];
            GridView1.DataBind();

Answer 1

You have set the captions to “Max” and “Min”, but the DataColumns's identifier is it’s Ordinal or ColumnName. You have set the ColumnName via constructor to

"Most Expensive Product" and "Least Expensive Product"

So use

string expr = "[Most Expensive Product] * [Least Expensive Product]";

instead.