create table tab_1 (
field_1 number,
field_2 number);

create table tab_2 (
field_1 number,
field_2 number,
field_3 number,
field_4 number);

SELECT t1.field_1, res.field_1, res.field_2
from tab_1 t1, (SELECT t2.field_1, t2.field_2
              FROM tab_2 t2
               WHERE t2.field_3 = 1
                UNION
             SELECT t22.field_1, t22.field_2
              FROM tab_2 t22
               WHERE t.22field_3 = 2
               AND t.22field_4 = t1.field_2) res