Following code illustrates how we can use SysQuery::countTotal() method to get the number of records in Query.
static void Query_cntRecords(Args _args)
{
Query query = new Query();
QueryRun queryRun;
QueryBuildDataSource qbd;
;
qbd = query.addDataSource(tablenum(CustTable));
queryRun = new QueryRun(query);
info(strfmt("Total Records in Query %1",SysQuery::countTotal(queryRun)));
}