insert into tb_nfe
    (id_emp, id_nf, sit, descr_sit_nfe, id_sit_nfe)
select 
    id_emp, id_nf, '8', 'Autorizado o uso da NF-e', 100
from tb_nf
where
    not exists (select 1
                from tb_nfe as nfe1
                where
                    nfe1.id_emp = tb_nf.id_emp
                    and nfe1.id_nf = tb_nf.id_nf)
    and tb_nf.dt_emis between '2014-01-01' and '2015-12-01'
    and tb_nf.tp_emis = '[P]'
    and tb_nf.tp_op = '[S]'