[RS] Does cognos aggregate after or before rolling up

[dxwallace]

I never seem to get a definitive answer to this basic question, but if you have a calculation   (a * b) / c   does cognos roll up the data and then perform the calculation, or is the calculation performed on each detail line first and then rollup?

[blom0344]

IMHO performing a roll-up before performing the calculation would yield incorrect results in any case.

Example:

A             B            C          (A*B/C)

10           10          5            20
3            200        60           10
100        50         500          10
                                          ____
                                           40

Now a roll-up would be : (113*260/565 = 52)

But perhaps I am missing your point?

[dxwallace]

You have the point, I was finding my way through all the Aggregate and Rollup functionality.

Total, Calculate, Summary, Count and so on. I was getting some weird results in a report, so I had to start from scratch and see how cognos is calculating the data.

[goose]

it depends on the aggeration type set for the data item. In your example if the aggeration type was set to total like blom0344 said you would get the incorrect result. But if you set the aggeration type to aggregate cognos would rollup the values first and then perform bomdas giving you the correct result.