SQL & PL/SQL

hi

I have two tables and i want to join them using left join based on string concatenation as per limitation of my application i can only use it after where clause like below

create table shav_test1 (idd varchar(20), sec int, qty float )


insert into shav_test1 values ('1aa',2,100);
insert into shav_test1 values ('1bb',3,100);
insert into shav_test1 values ('1cc',4,100);
insert into shav_test1 values ('1dd',5,100);
insert into shav_test1 values ('2ee',2,100);
insert into shav_test1 values ('3ff',2,100);
insert into shav_test1 values ('4gg',2,100);

create table shav_test2 (id1 varchar(10),id2 varchar(10), sec int, qty float )

insert into shav_test2 values ('1','aa',2,100);
insert into shav_test2 values ('2','ee',2,100);
insert into shav_test2 values ('3','cc',2,100);
insert into shav_test2 values ('1','dd',5,100);

select * from shav_test1 s1, shav_test2 s2 where
s1.idd=(s2.id1||id2)(+)

I am getting error using above sql.

Please help
Thanks