Ok, I am really speeding up my queries (by 1/1000ths of second -_-)with
two table? I thought it would be the inverse...how come?

And about the storage, why would it take more space? I mean, if I have
4 incomes and 4 costs splitted into two tables, it's about the same
amout of data as 4+4 rows in the same table (I suppose the only
difference is one bit for each row for the 1 table layout VS some tiny
space used for the definition of one more table in the 2 tables
layout?)

The point here is I want to get to know these little subtleties...

thanks for your advice!

ibiza