We recently had to revisit one of the reports of our system (a financial solution) because it was taking too long, anywhere between 20 to 40 minutes depending on the size of the Mutual/Hedge Fund Company). Basically, the report contained information about the positions of each account in a fund, things like Units held, Average Cost, Market Value, Series. Unfortunately, these numbers cannot be obtained through simple SQL aggregation functions like SUM or AVG and crunching the numbers results in an exercise a little harder than that which includes going through the transactions history of each account.
