What I'm trying to do:
Customer can pick two dates and the following gets calculated:
sum (all registration before date1) - sum (all registration before date2)
How is this normally achieved without extensions? And if extensions are recommended which one?
The best I could think of myself is an extra table with dates in which the user can choose a period. And use the min and max date from that period as date1 and date2.
Any ideas/thoughts are welcome and very much appreciated.