subtract quantity or update table using sql code

[abcd_2014]

friends i have this table

itemID     quantity   invoice No 
1	      20	      156651
1	      10              56151
1	      5              33000
5	      15            5465465
5	       4             465465 
5	      8              4654654
6	       7             454654
6	      2               44558
6	      5                44

and a have wpf forms
contain button and text box and combo box to select itemid

i want using sql code
to subtract quantity from quantity table by using a textbox on wpf forms
with condition
for example if i enter 25 in a text box on wpf form
for itemid1
the code will check itemid and subtract for example 20 from first itemid (1) and 5 from second itemid (1) and so on


i work on the above
and i create this code

but not work with me
the foreach
loop for one row only
not all row

can you please give me guide line to correct this code

 private void btnOpenUnits_Copy_Click(object sender, RoutedEventArgs e)
        {
            dblQuantity = Convert.ToDouble(this.Quntity.Text);
            
            dataConnection GetQuantity = new dataConnection();
            DataTable table = GetQuantity.loadingdata("SELECT Top 5 StoreTransAction.ItemID, StoreTransAction.UnitID, StoreTransAction.quantity,StoreTransAction.StoresTransactionID, StoreTransAction.InvoiceNo  FROM StoreTransAction Where StoreTransAction.TransID = 1 And StoreTransAction.ItemID =@ItemID And StoreTransAction.UnitID =@UnitID Order by StoreTransAction.quantity DESC ;", this.cboItemName.SelectedValue, this.cboUnits.SelectedValue);  // Get the data table.
            dataGridtry.ItemsSource = table.DefaultView;

            foreach (DataRow row in table.Rows) // Loop over the rows.
            {
                if (dblQuantity <= 0)
                {
            
                    return;
                }

                
                    if (dblQuantity >= Convert.ToDouble(row.ItemArray[2].ToString()))
                    {



                        dataConnection UpdateQuantity = new dataConnection();
                        string[] para = { "@RowQantity", "@itemID", "@StoreId", "@UnitID", "@StoresTransactionID" };
                        object[] val = { dblQuantity, this.cboItemName.SelectedValue, this.cboStore.SelectedValue, this.cboUnits.SelectedValue
                                        , Convert.ToDouble(row.ItemArray[3].ToString()) };
                        UpdateQuantity.EditRecord("Update StoreTransAction SET StoreTransAction.quantity =[StoreTransAction].[quantity]-@RowQantity Where StoreTransAction.TransID = 1 And StoreTransAction.ItemID=@itemID And StoreTransAction.StoreID=@StoreId And StoreTransAction.UnitID=@UnitID And StoreTransAction.StoresTransactionID=@StoresTransactionID; ", para, val);
                        dblQuantity = dblQuantity - Convert.ToDouble(row.ItemArray[2].ToString());
                     
                    }
                    else 
                    {
                        
                        dataConnection UpdateQuantity = new dataConnection();
                        string[] paraelse = { "@dblQuntity", "@itemID", "@StoreId", "@UnitID", "@StoresTransactionID" };
                        object[] valelse = { dblQuantity, this.cboItemName.SelectedValue, this.cboStore.SelectedValue, this.cboUnits.SelectedValue, Convert.ToDouble(row.ItemArray[3].ToString()) };
                        UpdateQuantity.EditRecord("Update StoreTransAction SET StoreTransAction.quantity =[StoreTransAction].[quantity]-@dblQuntity Where StoreTransAction.TransID = 1 And StoreTransAction.ItemID=@itemID And StoreTransAction.StoreID=@StoreId And StoreTransAction.UnitID=@UnitID And StoreTransAction.StoresTransactionID=@StoresTransactionID;", paraelse, valelse);
                        dblQuantity = 0;
                    }
                

            }
            
        }