Error while performing compute SUM() in a column

Question

I've tried to compute a column in my datagrid, i will be showing these in my code as per below. I Keep getting these error.

I've go through these links
1. How To Convert The DataTable Column type?
2. Error while taking SUM() of column in datatable
3. Invalid usage of aggregate function Sum() and Type: String

//This is the column i add into my datagrid
MITTRA.Columns.Add("Min_Tol");
MITTRA.Columns.Add("Max_Tol");
MITTRA.Columns.Add("Min_Weight");
MITTRA.Columns.Add("Max_Weight");

// The following codes is working finely
// if you notice MTTRQT column, it's a data queried from database
for (int i = 0; i <= MITTRA.Rows.Count - 1; i++)
{
    string item = MITTRA.Rows[i]["MTITNO"].ToString();

    Tolerancechecking = database_select4.LoadUser_Tolerance(item);

    MITTRA.Rows[i]["Min_Tol"] = Tolerancechecking.Rows[0]["Min_Tol"].ToString();
    MITTRA.Rows[i]["Max_Tol"] = Tolerancechecking.Rows[0]["Max_Tol"].ToString();

    MITTRA.Rows[i]["Min_Weight"] = Convert.ToDecimal(MITTRA.Rows[i]["MTTRQT"]) - ((Convert.ToDecimal(MITTRA.Rows[i]["MTTRQT"]) * Convert.ToDecimal(MITTRA.Rows[i]["Min_Tol"]) / 10));
    MITTRA.Rows[i]["Max_Weight"] = Convert.ToDecimal(MITTRA.Rows[i]["MTTRQT"]) + ((Convert.ToDecimal(MITTRA.Rows[i]["MTTRQT"]) * Convert.ToDecimal(MITTRA.Rows[i]["Max_Tol"]) / 10));

    dataGrid2.Columns.Clear();
    dataGrid2.ItemsSource = null;
    dataGrid2.ItemsSource = Tolerancechecking.DefaultView;

}


//Working Sum computation
Decimal Sum = Convert.ToDecimal(MITTRA.Compute("SUM(MTTRQT)", string.Empty));  
MaxTol.Text = Sum.ToString();  /*** This is working as i got my value on the text box ****/

Errors when trying sum computation for different column Initial try

  1. Decimal Sum = Convert.ToDecimal(MITTRA.Compute("SUM(Min_Weight)", string.Empty));

Errors occurred

Invalid usage of aggregate function Sum() and Type: String.

Second Attempts

  2.  Decimal Sum = Convert.ToDecimal(MITTRA.Compute("SUM(Convert(Min_Weight,'System.Decimal'))", string.Empty));
  3.  Decimal Sum = Convert.ToDecimal(MITTRA.Compute("SUM(Convert(Min_Weight,'System.Decimal'))", ""));

Errors occurred

Syntax error in aggregate argument: Expecting a single column argument with possible 'Child' qualifier.

How am i going to get the compute sum function to work?

Answer 1

Thank you @NoChance for the solutions. Hope this post can help others too.

/***** This is the part where i declare my datacolumn data type ****/
DataColumn Min_Weight = new DataColumn("Min_Weight");
Min_Weight.DataType = System.Type.GetType("System.Decimal");
MITTRA.Columns.Add(Min_Weight);

/**** This Works finally *****/ 
Decimal Sum = Convert.ToDecimal(MITTRA.Compute("SUM(Min_Weight)", string.Empty)); 
MaxTol.Text = Sum.ToString();