trigger-procedure without plpgsql

Hi all,
I!m having a hard time getting out well with trigger-procedures without using plpgsql. I cannot put a hand on some documentation about writing procedures in LANGUAGE 'sql'. There must be some info somewhere, isn't it?
Anyway, if someone can help...
I am trying to make a procedure which can update a table as reaction to an insert into another table. For that, I need to get the id of the table to update but I can't get it in any way because I don't know how to call it. The "new.id_table_to_update" doesn't seem to be recognized (the "new" term into the 'sql' procedure doesn't seem to be the right syntax to reference it).

I would like to use 'sql' language for that 'cause I don't see any interest in doing it with plpgsql if I can do it without it.
If someone could help... or at least mention some place where to learn how to do this, I would be very glad.

Thanks,
Picrate