Submitting this as a feature request because I can't find an existing request for this functionality and it would really help in a lot of different use-cases:
We need a way to control date granularity on views aggregation settings. Currently date fields aggregate at the lowest level of the date field, which makes aggregation essentially useless when you want to aggregate on a date field. For example: I have nodes with a year-month-day date field and I want a simple view that shows me how many nodes exist with date field values for each year. I want:
2012: 47 nodes
2011: 122 nodes
2010: 34 nodes
I dive in and configure my view, setting up the typical aggregation settings needed for this type of thing. I hit a snag when I realize that the view is grouping on the full date field, aggregating only the rows that have the exact same month/day/year.
Something like http://drupal.org/project/views_date_format_sql, only for date module fields, not just system dates.
If anyone can inform me on how to aggregate my date field values by year only, that would be awesome; we can close this request.