Aggregation: DECODE & CASE calculations returns different values between Discoverer Plus and Discoverer Desktop 10.1.2

(This post does not want to discuss how aggregation works, it assume that you already knows aggregation behavior, but it gives you solution to most known scenarios)

From Discoverer 9.0.2 and above i.e Discoverer 9.0.4 and Discoverer 10.1.2 has enhanced roll-up and calculation capabilities a feature called Enhanced Data Aggregation where when connected to a 9.0.1.4 or higher database, the Discoverer server will rely on the CUBE, ROLLUP and GROUPING SET database functionality to compute roll-up values. This new capability correctly handles many of the restrictions described in the provided note, so that a roll-up value can be computed where the 4i server would have to resort to using the "N.A" string.

Additionally, enhanced Data Aggregation is present only in the Discoverer Middle-tier(Plus and Viewer) server -- Not Discoverer Desktop. You will see aggregations in Plus and Viewer that show up as "N/A" in Desktop.

By the way, we can define:

Linear Calculation
A calculation for which the aggregate value is same as the value obtained by summing up the individual values is a linear calculation.

Locally computable Calculation
Discoverer can locally compute all primitive arithmetic operations (+, -, *, / etc), a subset of aggregates (Sum, Sum_Squares, Count, Max, Min, Average and Variance), some string operators, and Decode. Discoverer can locally compute most calculations that can be broken down into linear parts and that involve the above set of operators.
Calculations such as Sum (Profit) / Count (Profit) can be locally computed as it can be broken down into two Linear Parts Sum (Profit) and Count (Profit) combined by the division operator. Calculations such as Sum (Profit) / Count_Distinct (Profit) cannot be locally computed as one of the parts (Count_distinct (Profit)) is not Linear.

Non-Aggregable Calculation
A pre Oracle 9i database allows data to be fetched at only one level of aggregation. From this data discoverer has to compute values at higher levels of aggregation to support things like totals, outline values etc. This is possible only if the calculation is either Linear or Locally computable.
If a calculation is neither linear nor locally computable it will be marked as non-aggregable. The value specified in the option “Show non aggregable values as “ is displayed for such cells.

Case / Decode
Totals on aggregate calculations involving a case expression might yield non-intuitive results. This is because the item values involved in the condition part of the case expression will become NULL when they are rolled up on that item.



In most of cases the solution is to add in the PC Client where Discoverer Desktop is installed regedit entries, like:

o Add two DWORD values named: AggregationBehavior & AllowAggregationOverRepeatedValues = 1 under the key: HKEY_CURRENT_USER\Software\ORACLE\Discoverer 10\Application\ and set both to 1;

Then, Discoverer Desktop should be closed and re-launched.