Question

I have my codes here without errors (at least not when I Debug it, I use VS 2010), but what I wish to happen is when I click on the add button, the number/s in the textbox(txtQty) would add to the numbers currently saved in the column “Quantity”. (ex: txtQty “100” and current on the column is “200”, I want to add “100” from the textbox to the column which has “200” and save it as a new number “300”. Simple math I know, but the problem is I have yet to know how to use math equations on VB.NET Datagridview or MySql Database This Code executes but when I click Add the numbers in the column return to 0. Any Hint or Tips would be much appreciated, thanks.

        cmd.Connection = conn

        Dim Result = "Quantity" + txtQty.Text

        cmd.CommandText = " UPDATE incomingdeliveries SET Quantity ='" & Result & "';"
        cmd.Parameters.Add(New MySqlParameter("@Quantity", txtQty.Text))

        cmd.ExecuteNonQuery()

        MsgBox("Data Added to the Database")

            Me.IncomingdeliveriesTableAdapter.Dispose()
        Me.IncomingdeliveriesTableAdapter.Fill(Me.IncomingDeliveriesDataSet.incomingdeliveries)

            lblCode.Text = ("Tables Refreshed!")

Answer 1

your command text must be parameterized also

cmd.CommandText = " UPDATE incomingdeliveries SET Quantity = @iQuantity + Quantity"
cmd.Parameters.Add(New MySqlParameter("@iQuantity", txtQty.Text))

UPDATE 1

Using _conn As New MySqlConnection("connectionStr here")
    Using _comm As New MySqlCommand()
        With _comm
            .Connection = _conn
            .CommandText = "UPDATE incomingdeliveries SET Quantity = @iQuantity + Quantity"
            .CommandType = CommandType.Text
            .Parameters.AddWithValue("@iQuantity", txtQty.Text)
        End With
        Try
            _conn.Open()
            _comm.ExecuteNonQuery()
        Catch ex As MySqlException
            Msgbox(ex.Message.ToString())
        End Try
    End Using
End Using