คำแนะนำ

- แสดงการทำงานร่วมกันของ listbox combobox และ datagridview

- การนำข้อมูลจาก northwind.mdb ใส่เข้าไปใน windows control

- การเลือกข้อมูลตามลำดับชั้น ผ่านคำสั่ง select * from ... where ...

- มี Windows Form : nwindnet1  (4 KB) ให้ฝึกการ Add เข้า Windows Application

Imports system.data.oledb
Public Class nwindnet1
    Dim strdb As String = "c:\northwind.mdb"
    Dim strconn As String = "provider=microsoft.jet.oledb.4.0;data source=" & strdb
    Dim strsql As String
    Dim cn As New System.Data.OleDb.OleDbConnection(strconn)
    Dim cm As New OleDbCommand(strsql, cn)
    Dim dr As OleDbDataReader
    Private Sub nwindnet1_Load(ByVal sender As Object, _
	ByVal e As System.EventArgs) Handles Me.Load
        read_mdb()
    End Sub
    Sub read_mdb()
        ListBox1.Items.Clear()
        strsql = "select categoryid,categoryname from categories"
        cm = New OleDbCommand(strsql, cn)
        cn.Open()
        dr = cm.ExecuteReader()
        While dr.Read()
            ListBox1.Items.Add(dr.Item("categoryid") & "," & dr.Item(1))
        End While
        cn.Close()
    End Sub
    Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, _
	ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
        ComboBox1.Items.Clear()
        strsql = "select * from products where categoryid=" & Split(ListBox1.Text, ",")(0)
        cm = New OleDbCommand(strsql, cn)
        cn.Open()
        dr = cm.ExecuteReader()
        While dr.Read()
            ComboBox1.Items.Add(dr.Item(0) & "," & dr.Item(1))
        End While
        cn.Close()
        ComboBox1.Select()
        ComboBox1.Text = ComboBox1.Items.Item(0)
    End Sub
    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As Object, _
	ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        ComboBox2.Items.Clear()
        strsql = "select * from [order details] "
        strsql &= "where productid = " & Split(ComboBox1.Text, ",")(0)
        cm = New OleDbCommand(strsql, cn)
        cn.Open()
        dr = cm.ExecuteReader()
        While dr.Read()
          ComboBox2.Items.Add(dr.Item(0) &","& dr.Item(1) &","& dr.Item(3))
        End While
        cn.Close()
        ComboBox2.Select()
        ComboBox2.Text = ComboBox2.Items.Item(0)
    End Sub
    Private Sub ComboBox2_SelectedIndexChanged(ByVal sender As System.Object, _
	ByVal e As System.EventArgs) Handles ComboBox2.SelectedIndexChanged
      ComboBox3.Items.Clear()
      strsql = "select * from [orders] "
      strsql &= "where orderid = " & Split(ComboBox2.Text, ",")(0)
      cm = New OleDbCommand(strsql, cn)
      cn.Open()
      dr = cm.ExecuteReader()
      While dr.Read()
        ComboBox3.Items.Add(dr.Item(0) &","& dr.Item(1) &","& dr.Item(2) &","& dr.Item(3))
      End While
      cn.Close()
      ComboBox3.Select()
      ComboBox3.Text = ComboBox3.Items.Item(0)
    End Sub
    Private Sub ComboBox3_SelectedIndexChanged(ByVal sender As System.Object, _
	ByVal e As System.EventArgs) Handles ComboBox3.SelectedIndexChanged
      Dim x As Integer = DataGridView1.Columns.Count()
      Dim i As Integer = 0
      For i = 0 To x : DataGridView1.Columns.Clear() : Next
      strsql = "select * from employees "
      strsql &= "where employeeid = " & Split(ComboBox3.Text, ",")(2)
      cm = New OleDbCommand(strsql, cn)
      cn.Open()
      dr = cm.ExecuteReader()
      If dr.Read() Then
        x = DataGridView1.Rows.Count()
        DataGridView1.Columns.Add("eid", "eid")
        DataGridView1.Columns.Add("ename", "ename")
        DataGridView1.Rows.Add()
        DataGridView1.Rows(x).Cells(0).Value = dr.Item(0)
        DataGridView1.Rows(x).Cells(1).Value = dr.Item(1)
      End If
      cn.Close()
    End Sub
End Class