GROUP BY

Hello, I am a student at a university in France. I work on MonetDB, Windows platform. I have some questions: I want to optimize the "Group by" function of the SQL module in order to create a new function combining the "Group by" function and another function. For this I want to know: 1 - How to locate the class containing the code of the "Group by" function 2 - How to edit the code in question to change it 3 - Which editor should be used to compile the project. 4 - I tried to use "Visual Studio 2012" to open the project "MonetDB" but I have not managed to do. Regards Ahmed Bouslah.