insert into tb_item_emp
    (id_item, id_emp, vl_prc_vnd)

select
    tb_item.id_item,
    1,
    0
from tb_item
where
    not exists (select 1
                from tb_item_emp e1
                where
                    e1.id_item = tb_item.id_item and
                    e1.id_emp = 1)
                    