Aggregation in script HELP

[#1]

Hello People,

I have to make some aggreagation in my script,
Here is my script :

The field [Identifiant] is just a ID
              [Pose / Dépose] can only take to string value : 'Pose' and 'Dépose' ;

             [ETI] can take lot value pas what's important for me is also two values lets say 'ar' and 'st'

             [Nature] can take 21 values lets say Nature_1, Nature_2... Nature_21; but in reallity i

             [Qté prévue] is quantiy is a numeric value
             [Année de construction] containt year but its not important for me yet.

What i want to do  is sum([Qté prévue]) but with some conditions :

First i'm not interressed by sum([Qté prévue]) for each Nature( 1, 2...21) separatly , but im interressed in :
                                    
                                                        sum([Qté prévue]) for a groupe of [Nature] together

For exemple a field called [Qté Prevue (Nature-1-2-3)]  that containt sum([Qté prévue]) where [Nature]= {Nature_1, Nature_2, Nature_3}.

another  field called [Qté Prevue (Nature-5-6-8)]  that containt sum([Qté prévue]) where [Nature]= {Nature_5, Nature_6, Nature_8}.

And i want lets say  [Qté Prevue (Nature-1-2-3) & Pose]  where [Pose / Dépose]= 'Pose'
and [Qté Prevue (Nature-1-2-3) & Dépose] where [Pose / Dépose]= 'Dépose' . i want that also for [Qté Prevue (Nature-5-6-8) Pose] and [Qté Prevue (Nature-5-6-8) Dépose]....

Once have that i want  [Qté Prevue (Nature-1-2-3) & Pose & ar] where [ETI]= 'ar' aand [Qté Prevue (Nature-1-2-3) & Pose & st] where [ETI]= 'st'.

I would like to do in a script for performance purpose.

Thanks and ask me if you didnt understant well.

Thanks you.