我想从不同的表调用数据

Question

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    Try
        con.Open()
        cmd.Connection = con
        cmd.CommandType = CommandType.Text
        cmd.CommandText = "SELECT * FROM guestdatabase "
        dr = cmd.ExecuteReader
        While (dr.Read())
            Dim nems = dr.GetString("Name")
            Visitor.Items.Add(nems)
        End While
    Catch ex As Exception
        MessageBox.Show(ex.Message)
        con.Close()
    End Try

End Sub

Private Sub Fname_TextChanged(sender As Object, e As EventArgs) Handles Fname.TextChanged

    Try
        con.Close()
        con.Open()
        cmd.Connection = con
        cmd.CommandType = CommandType.Text
        cmd.CommandText = "SELECT * FROM residents WHERE FirstName = '" & Fname.Text & "'"
        dr = cmd.ExecuteReader
        If Not dr Is Nothing Then
            dr.Read()
            Lname.Text = dr("LastName").ToString
            dr.Close()
        End If
    Catch ex As Exception
        MessageBox.Show(ex.Message)
        con.Close()
    End Try

End Sub

我想在1个表单中同时调用来自不同表的数据，但是它表示“从组合框调用Read（）1之前访问字段的无效尝试和文本框中的1请求帮助：3提前谢谢