Exception: No value given for one or more required parameters in VB.NET & MS-ACCESS DB

问题

I work with an Inventory System. I have an error on my code, it says

No value given for one or more required parameters.

and the error was thrown to cmd.ExecuteNonQuery(). What does it mean? can someone help me? By the way this code is for deducting Item Quantity on Database. Sorry for my bad English.

con.Open()
Dim sqlQry As String = "UPDATE [tbl_Stocks] 
                        SET [Quantity] = [Quantity] - @QU 
                        WHERE Products='" & lbPro.Text & "'"
Using cmd As New OleDbCommand(sqlQry, con)
    cmd.Parameters.AddWithValue("@QU", lbQuan.Text)
    cmd.ExecuteNonQuery()
    con.Close()
    MsgBox("Save Successfully!")
End Using

回答1:

I don't see any flaw. Try this substitute(a little tweak sending both inputs via parameter)

con.Open()
Dim sqlQry As String = "UPDATE [tbl_Stocks] SET [Quantity] = [Quantity] - @QU " &
                       "WHERE Products=@prod"
Using cmd As New OleDbCommand(sqlQry, con)
    cmd.Parameters.AddWithValue("@QU", lbQuan.Text)
    cmd.Parameters.AddWithValue("@prod", lbPro.Text)
    cmd.ExecuteNonQuery()
    con.Close()
    MsgBox("Save Successfully!")
End Using

来源：https://stackoverflow.com/questions/38738490/exception-no-value-given-for-one-or-more-required-parameters-in-vb-net-ms-acc