Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        
        Dim g1 As String
        ComboBox2.Items.Clear() 'refresh combo sem 
        g1 = ComboBox1.Text
        Dim MyCmd As New OleDbCommand
        Dim MyReader As OleDbDataReader        
        con.Open()

        MyCmd.Connection = con
        MyCmd.CommandType = CommandType.Text
        MyCmd.CommandText = "select DISTINCT CourseID from Course  where  LevelNo='" & g1 & "'"
        MyReader = MyCmd.ExecuteReader

        Do While MyReader.Read
            ComboBox2.Items.Add(MyReader.GetString("0")) 'this statment select only 1 (0)coulmn in table
        Loop
        MyReader.Close()
        con.Close()
    End Sub

MyCmd.CommandText = "select DISTINCT CourseID from Course  where  LevelNo=" & g1

Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged        
        Dim g1 As String
        ComboBox2.Items.Clear() 'refresh combo sem 
        g1 = ComboBox1.Text
        Dim MyCmd As New OleDbCommand
        Dim MyReader As OleDbDataReader
        MyCmd.Connection = con
        MyCmd.CommandType = CommandType.Text
        MyCmd.CommandText = "select DISTINCT CourseID from Course  where  LevelNo='" & g1 & "'"
        con.Open()
        MyReader = MyCmd.ExecuteReader
        Do While MyReader.Read
            ComboBox2.Items.Add(MyReader.GetString("0")) 'this statment select only 1 (0)coulmn in table
        Loop
        MyReader.Close()
        con.Close()
End Sub

'create a connection using a class Named "MainConn"
Public Class MainConn
    Public Shared strconn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Application.StartupPath & "\Video.mdb;Persist Security Info=False;"   

End Class

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Private Sub Payment_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
       
Dim conn As New OleDbConnection(MainConn.strconn)
        conn.Open()
        Dim objReader As OleDb.OleDbCommand = New OleDb.OleDbCommand("select date from Transactions where amount=0 order by tid asc", conn)
        Dim rd As OleDb.OleDbDataReader
        rd = objReader.ExecuteReader()

        Do While rd.Read()
           
            cmbdate.Items.Add(rd("tid".ToString))
        Loop
        rd.Close()
        conn.Close()

end sub