Hello. Could you do me a faver?
I know how can I use FOMULA function to calculate sum of column .
Col Sum(:ASSY_IN_QTY)
Furthermore, I want to calculate sum of column by cust (customer name)

I want to make script more simply from your answer.
Thanks.
dt << New Column( "Col Sum by customer",
Numeric,
Continuous,
formula(
Col Sum(:ASSY_IN_QTY)
)
);