随机生成的值如何自动更新到表的指定字段？

Dim K, a, b, I, Num, X, P As Integer
    Dim str, Pa As String
    str = ""
    For I = 1 To 12
        P = Int(Rnd * 2) '随机产生0，1两个随机数，使得数字与字母的顺序不同
        If P = 0 Then    '如果为0那就产生数字，反之产生字母
            Num = Int(Rnd * 10)  '随机产生0-9的随机数
            Pa = Num
        Else
            K = Int(Rnd * 1)    '1大写，2小写
            Select Case K
          
            Case 0: a = 65: b = 90
            Case 1: a = 97: b = 122
            End Select
            X = Int(Rnd * (b - a + 1) + a)    'a-b随机数
            Pa = Chr(X)    '随机对应的AscII字符
        End If
        str = str & Pa

    Next I
    str = "1006AA" & Left(str, 6) & Right(str, 6)
    Me.Text1 = str
    DoCmd.SetWarnings False
    DoCmd.RunSQL "UPDATE acd SET acd.[key] ='" & Me.Text1 & "';"
    DoCmd.SetWarnings True

但表中至少要一条记录