如何通过ADO使用聚合函数来查询(数据库为ACCESS)

_RecordsetPtr CMyAdo::SelectRecord(string &where, string &tablename,string &field, int way )
{
    int ret = 0;
  _RecordsetPtr pset;
CString  sql;
    VARIANT  count;
count.vt = VT_INT;
ret = OpenDB();
if( ret == 1 )
return -1;                    //创建对象失败
else if( ret == 2 )
  return -2;                    //数据库打开失败
try
{

    sql.Format("select count(*) from %s", tablename.c_str() );

    /*if( way == 0 )          //查询全部
{
sql.Format("select  * from %s", tablename.c_str() );
    TRACE("sql = %s\n",sql);
}
else if( way == 1 )      //按字段查询
sql.Format("select %s from %s", field.c_str(), tablename.c_str() );
else if( way == 2 )      //按条件全部查询
{

}
else if( way == 3 )      //按条件和字段联合查询
{

}*/
pset = m_dbptr->Execute((_bstr_t)sql.GetBuffer(sql.GetLength()),&count,adCmdUnknown);
if( pset != NULL && !pset->ADOEOF )
retu