vb.net做了一个注册窗口，运行通过，但总是添加失败

VB.NET code

 Private Sub addBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles addBtn.Click        If txtuser.Text.Trim = "" Then            MessageBox.Show("用户名不能为空")        ElseIf txtpassword.Text = "" Then            MessageBox.Show("密码不能为空")             Exit Sub        End If        If o.AddUser(txtuser.Text.Trim(), txtpassword.Text。trim（）) Then            MessageBox.Show("添加成功!")            Me.Close()        Else            MessageBox.Show("添加失败!")        End If    End Sub Public Function AddUser(ByVal id As String, ByVal password As String, ByVal name As String) As Boolean        Dim dt As DataTable = o.GetDataTable("SELECT * FROM zhanghao WHERE id='" & id & "'")        Dim SQL As String        SQL = "INSERT INTO zhanghao(id,password,z_name) values('" & id & "','" & password & "','" & name & "')"        Return o.ExecuteSQL(SQL)    End Function