获取列和在vb.net中的文本框中输入的值的总和

Question

i have a textbox named AddU.text, i also have a msaccess table field named Quantity, what I want is that when i input a value in AddU.Text and click the add button, the value i entered will be automatically add to the existing value in Quantity. I keep searching for solution but can't find the right one. Can anyone help me? Heres my current codes:

Dim cmd As New OleDb.OleDbCommand
    If Not conn.State = ConnectionState.Open Then
        conn.Open()
    End If
    Try
        cmd.Connection = conn
        cmd.CommandText = "UPDATE BC_Inventory SET [Addition]='" + AddU.Text + "'," + _
        "[Date_Updated]='" + DateU.Text + "',[Time_Updated]='" + TimeU.Text + "',[Updated_By]='" + UpdatedBy.Text + "'" + _
        "WHERE [Item]='" + com_ItemU.Text + "'"
        cmd.ExecuteNonQuery()




    Catch ex As Exception
        MessageBox.Show(ex.Message, "Error")
    Finally
        conn.Close()
    End Try

actually i still have no codes for it, i keep trying the codes i found in researching but nothing helps thats why i deleted it.

Answer 1

I suspect that your quantity-field is a field in your table? This is the changed SQL-Query.

Dim cmd As New OleDb.OleDbCommand

If Not conn.State = ConnectionState.Open Then
    conn.Open()
End If

Try
    ' SQL-Query with Database Update on Field Quantity = Quantity + AddU.Text
    Dim strSQL As String = "" & _
        "UPDATE BC_Inventory " & _
        "SET [Addition]     = '" & AddU.Text & "', " & _
        "    [Quantity]     = CDbl([Quantity]) + CDbl(" & CDbl(AddU.Text.Replace(",", ".")) & "), " & _
        "    [Date_Updated] = '" & DateU.Text & "', " & _
        "    [Time_Updated] = '" & TimeU.Text & "', " & _
        "    [Updated_By]   = '" & UpdatedBy.Text & "' " & _
        "WHERE [Item] = '" & com_ItemU.Text & "' "

    ' For Debugging
    ' MsgBox(strSQL)

    cmd.Connection = conn
    cmd.CommandText = strSQL
    cmd.ExecuteNonQuery()
Catch ex As Exception
    MessageBox.Show(ex.Message, "Error")
Finally
    conn.Close()
End Try

Edit 1 : A " sign was double in the line "WHERE [Item] ..."

Edit 2 : Changed Convert(DOUBLE, Quantity) to Convert(DOUBLE, [Quantity])

Edit 3 : Remark for debugging.

' For Debugging
' MsgBox(strSQL)

Edit 4 : Added the missing ) to Convert(DOUBLE, '" & CDbl(AddU.Text) & "', " right at the end.

Edit 5 : changed )' to ')

Edit 6 : Now with CDec() instead of Convert(Double, )

Edit 7 : CDbl(AddU.Text.Replace(",", "."))

Edit 8 : Removed the ' around the CDbl(AddU.Text)

Edit 9 : replaced the CDec with CDbl