Private Sub Combo1_Click()
    Dim SQLString As String

    flgClient.Visible = False
    
    Set adoRecordset = New ADODB.Recordset
    
    Select Case Combo1.ListIndex
        Case  0 
            SQLString = "SELECT * FROM serial_number WHERE serial_number LIKE '%" & Txt1.Text & "%'"
        Case  1 
            SQLString = "SELECT * FROM serial_number WHERE ID LIKE '%" & Txt1.Text & "%'"
        Case  2 
            SQLString = "SELECT * FROM serial_number WHERE Users LIKE '%" & Txt1.Text & "%'"
        Case  3 
            SQLString = "SELECT * FROM serial_number WHERE Number_Auto LIKE '%" & Txt1.Text & "%'"
        Case Else
            SQLString = "SELECT * FROM serial_number"
    End Select
    
    adoRecordset.Open SQLString, adoConnection, adOpenStatic
    Txt1.Text = ""
    ShowIt
    flgClient.Visible = True

End Sub