สอบถามเรื่องการดึงค่าข้อมูลแสดงใน datagridview ตามความสัมพันธ์ข้อมูล

Imports System.Data.SqlClient
Public Class Form2
    Dim con As New SqlConnection
    Dim cmd As New SqlCommand
    Dim strsql As String
    Dim strsql1 As String
    Dim dt As New DataTable
    Dim dt1 As New DataTable
    Dim dtAdapter As SqlDataAdapter

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        strsql = "Data Source=localhost; Initial Catalog=KU_OCR; Integrated Security= true"
        con.ConnectionString = strsql
        con.Open()

        strsql = "Select * from Teacher"
        dtAdapter = New SqlDataAdapter(strsql, con)
        dtAdapter.Fill(dt)
        Me.DataGridView1.DataSource = dt
    End Sub

    
    Private Sub DataGridView1_CellClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellClick
        Dim aa As String
        If e.RowIndex = -1 Then Exit Sub
        With DataGridView1
            aa = .Rows.Item(e.RowIndex).Cells(0).Value.ToString
            TextBox1.Text = aa
            strsql1 = "Select * from Teaching where teac_id = '" & aa & "' "
            dtAdapter = New SqlDataAdapter(strsql1, con)
            dtAdapter.Fill(dt1)
            Me.DataGridView2.DataSource = dt1

        End With

    End Sub

End Class