MySQL / ASP Klasik - Kueri Berparameter

Kode di cuplikan kedua Anda sudah benar, tetapi harus diterapkan ke ADODB.Command baru objek, bukan ke Connection objek:

username = Trim(Request("username"))

'-----Added this-----
Dim cmdContent
Set cmdContent = Server.CreateObject("ADODB.Command")

' Use this line to associate the Command with your previously opened connection
Set cmdContent.ActiveConnection = connContent
'--------------------

cmdContent.Prepared = True

Const ad_nVarChar = 202
Const ad_ParamInput = 1

SQL = " SELECT * FROM users WHERE (username=?) ; "

Set newParameter = cmdContent.CreateParameter("@username", ad_nVarChar, ad_ParamInput, 20, username)
cmdContent.Parameters.Append newParameter

cmdContent.CommandText = SQL
Set rs = cmdContent.Execute

If NOT rs.EOF Then
        ' Do something...
End If

rs.Close

Omong-omong, ada kesalahan ketik dengan ejaan adParamInput bukannya ad_ParamInput (dikoreksi dalam contoh saya).