aggregation vs. roll-up aggregation functionality?

[rhythmz]

I hope this does not sound rhetorical, but can someone please explain aggregation vs. roll-up aggregation?

I ask this because if I create a calculation using the vendor-defined 'TOTAL' function....why or when would I then use the aggregation finctionality in Cognos 8?

We have a Cognos consultant on-site who has been unable to clearly contrast the two and\or when I should use them in Cognos vs. within a user-defined calculation. Could someone explain this concept or direct me to a site that I can research myself? I am failing to grasp this thus far using Cognos reseources alone. ;D

[blom0344]

You normally do not code TOTAL unless you need to add a context to the calculation. Setting the aggregate to TOTAL enforces the aggregate to be added to the generated SQL. This allows more flexibility, since changing the aggregate setting would allow for different aggregate behavior (without changing expressions)

If you create a query that fetches revenue by year and month, then revenue will be aggregated in the SQL against year and month. Create 2 lists based on the query (revenue by year/month  and  revenue by year) and Cognos will automatically roll up data to the year level in the list that contains just year and revenue

[peritas-chris]

The simplest way to describe it is:

'Aggregate Function' determines how detail values will be rolled up into non-grouped totals in your report.
'Roll-up Aggregate Function' determines how those non-grouped totals will be aggregated for summary (grouped) totals in your report. For example, you may choose to average summaries rather than simply add them up.

Let me know if I can help make this clearer, feel free to send me a message.

[james899]

I am not sure this totally explains it but would it help us both to have some groupings first to see how each aggregation acts?

My problem is twofold. I was trying to add aggregation on the summary line by using the dropdowns on the left pane for a field. Than never made it display so I was confused. I realized I had to use the icon in the top menu in page design view for the aggregation to show in the summary line. That is not intuitive!

I starting adding field aggregations but then I wanted to delete one and I do not know how. I tried highlighting and hitting delete or right-clicking and using cut but then it removes the whole summary line! How do I remove just one data item aggregation from the summary line?

[blom0344]

Select the unlock button (in the menu) and in unlock mode remove the aggregation from the line (delete or cut)
(Hope I understand you correctly   :)  )