Using a select query

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C#

How do I populate a listbox using select query (which stems from a combobox)

If 'multi ice cream' is selected in the combobox then I want the system to select that row and show me what is in the 'process' column in my listbox

so based on what the user select from the comboBox, you make a query and fill the ListBox with the result

So far the code is not returning anything, I'm not too sure why

MAcon.Open();
OleDbDataAdapter da = new OleDbDataAdapter("Select Process from [Product Family] Where [Product Name] = @ProductName", MAcon);
da.SelectCommand.Parameters.AddWithValue("@Process", ItemCBx.SelectedItem.ToString());
DataTable dtbl = new DataTable();
da.Fill(dtbl);

if (dtbl.Rows.Count == 1)
{
    Listbox1.Items.Add(dtbl.Rows[0][0]);
}

MAcon.Close();

What I have tried:

MAcon.Open();
OleDbCommand da = new OleDbCommand("Select Process from [Product Family] Where [Product Name] = @ProductName", MAcon);
OleDbDataReader sdr = da.ExecuteReader();
while (sdr.Read())
{
    Console.WriteLine(sdr[0].ToString());
}
MAcon.Close();