Raf,

I think you would get the result that you are looking for if you follow what DaPi has suggested. He has asked you to try this:

select a.ls_id, a.FL_ID,a.RM_TYPE,b.DV_ID,c.COD_RITMI,c.DESCR_RITMI,c.TIPO_SPAZIO
from cod_test a, dp_test b, ti_use_test c
where a.dv_id=b.DV_ID(+)
and a.RM_TYPE=c.RM_TYPE(+)
AND (B.SNOP='T03' or B.SNOP is NULL)