Johan Falk erklärt das Aggregation Feature in Views.
If you don’t want to watch screencasts, here’s short-short version (spoiler alert!):
- Aggregation makes Views not return items from the database, but groups of items.
- You find the aggregation setting in the advanced section in Views.
- Add any fields you want to use for grouping, in aggregation mode “group similar results”.
- Add any fields you want to do calculations on – sums, averages, counts, etc.
- Make sure you don’t, for example, have sorting on publish date – it will make your aggregation more or less meaningless.