Sum error

iam trying to add values from different fields based on eventNo but the problem is the in one table i need to add more then one thing, tryed doing this
SELECT (sum(ei.Quantity * e.Unit_price)+ v.cost_per_day )* (ev.end_date - ev.start_date )
FROM Equipment e, Equipment_invoice ei, Event ev, Venue_invoice vi, Venue v
WHERE (ei.EquipmentNo = e.EquipmentNo AND
ei.EventNo = ev.EventNo AND
ev.EventNo = vi.EventNo AND
ei.E_invoiceNo = ei.EventNo AND
vi.VenueNo = v.VenueNo) AND
(ei.Quantity * e.Unit_price+ v.cost_per_day * (ev.end_date - ev.start_date) > 10)
order BY ei.EventNo;

gives me a ERROR at line 1:
ORA-00937: not a single-group group function
how do i go about fixing this error?

The attached query is not tested but suppose to work. Also I am not sure that it is your required query or not because you did not write the basic concept or purpose of this query.

If you get any error or problem while running this query, let me know.


Regards,