void __fastcall TFormMain::Button1Click(TObject *Sender)
{

    AnsiString strDB =  ExtractFilePath(Application->ExeName) + "123.mdb";
    AnsiString strConn;
    if (FileExists( ExtractFilePath(Application->ExeName) + "123.mdb") == false)
    {
        ShowMessage("Could not connect the DateDase!");
        exit(0);
    }

    strConn.sprintf("Provider=microsoft.jet.oledb.4.0; Data Source=%s; Persist Security Info=False", strDB.c_str());
    FormMain->ADOConnection_DataBase->Connected =false;
    FormMain->ADOConnection_DataBase->ConnectionString = strConn;

    FormMain->ADOQuery_Login->SQL->Clear();
    FormMain->ADOQuery_Login->Close();
    FormMain->ADOConnection_DataBase->Connected =true;
    FormMain->ADOQuery_Login->SQL->Add("SELECT MAX(cardnum) FROM u_account" );
    //FormMain->ADOQuery_Login->ExecSQL();
    FormMain->ADOQuery_Login->Open();
    
    AnsiString s=FormMain->ADOQuery_Login->Fields->FieldByName("cardnum")->AsString;
    ShowMessage(s);
   
}
//---------------------------------------------------------------------------
我想得出cardnum的最大值，上面的代码执行时会出错误
请大侠们指教