Oracle's (+) notation within function
Is it still outer join? Or is it becomes inner join?


It is still an outer join:

SQL Fiddle

Oracle 11g R2 Schema Setup:

create table tab_a(num integer);
create table tab_b(num integer);

insert into tab_a(num) values(1);
insert into tab_a(num) values(2);

insert into tab_b(num) values(2);
insert into tab_b(num) values(3);


Query 1:

select *
from tab_a, tab_b
where tab_a.num = tab_b.num(+)


Results:

| NUM |    NUM |
|-----|--------|
|   2 |      2 |
|   1 | (null) |


Query 2:

select *
from tab_a, tab_b
where round(tab_a.num, 2) = round(tab_b.num(+), 2)


Results:

| NUM |    NUM |
|-----|--------|
|   2 |      2 |
|   1 | (null) |