How can I summarize and reuse a complex dataset - eclipse-plugin

Question

How can I re-use a single complex dataset across a number of tables?
The dataset has a number of computed columns that needs to be reported both in detail and in summary. Here's a very simplified example dataset:
is_food sale_association food_type total_sold total_associations percent_total
1 Before Movie Popcorn 50 3 x BirtMath.safeDivide(...)
0 Before Movie Soda 10 2 x BirtMath.safeDivide(...)
1 During Movie Jujubee 10 1 x BirtMath.safeDivide(...)
0 After Movie Soda 15 2 x BirtMath.safeDivide(...)
From this one dataset, I'd want to create a detailed summary of all food types while rolling up non food (using the 'is_food' column), another summary of all food types, another detailed summary of food with rolled up non-food by sale_association, etc. etc.
The report would also contain a number of percentages (6 in the most complex table) that need to be calculated (some across a row, others across all rows in a given group), all of which can have a zero value for the denominator and so need to be guarded against with safeDivide (which is a PITA to do in the source SQL query which itself is doing aggregation -- checking for divide by zero when both the numerator and denominator are sums leads to hairy queries).
Obviously I can do this by focusing the() SQL query as appropriate, but it seems like a waste of time and effort to create 12 or 15 queries that are very similar when I've already managed to create the monster query for the most detailed table.
What doesn't seem straightforward is how to perform the rollups in a table. I managed to hack something together by hiding rows that would later be summed up (e.g. "is_food == 0" in the example) and then creating custom data bindings that are displayed in a footer row. Not only does it feel like a hack, it also interferes with the ability to naturally order rows. Again, going back to the example, if I was ordering by total_sold and summarizing rows with is_food == 0, the natural order should be Popcorn, Non-food, Jujubee.
There's nothing in the BIRT wiki about this, nor does "BIRT: A Field Guide, 3rd E." really delve into the topic.

Answer 1

This seems like a fairly open-ended question (although I agree that re-using a single dataset makes much more sense than having multiple queries retrieving the same data in slightly different ways). A few general suggestions:
Use the most detailed version of the data required as a common dataset for each BIRT report item (typically BIRT tables)
Where summary-only level reporting is required, add groups to the BIRT table at the desired level, add data items as required to the group headers/footers and delete the detail level row(s) from the BIRT table.
Where detail-level reporting is required in some cases (eg. for food items but not for non-food items), add groups to the BIRT table as above, and set the visibility of the detail row (in Property Editor - Properties - Visibility) to check Hide Element, then specify the appropriate expression to suppress the non-required rows (non-food items, in this example).
Aggregations (ie. summary expressions) can be added to tables by selecting the whole table, selecting the Binding tab within the Property Editor and clicking the Add Aggregation... button.