thank you for your answer.
I understood the problem was different.
In my table1, I got a function like week(DATA) as week_grp, table2 joined with table1 also on DATA.
When I make a selection on week_grp the A;Pl_3 is kicked out.
Is there anything I can do in the join to avoid making week(DATA) also in table2?
it seems really weird to me, I thought functions like that would be considered just as attributes, and joining the table was enough to use them without replaying in the secondary table.