The best practice would be to try to break down all these queries to make a data model that only contains the relationship between tables. Aggregation should be done on the graphic side of QlikView and not pre-made in the script since QlikView is not a report generator.
However you should be able to paste the SQL statement into you load statement. For example,
SQL (Paste your statement);
If the ODBC or OLEDB supports the creation of temporary tables from nested selects then there should be no problem.