I did the following. Is it what you are aiming at (I assume you are user called BOSS)?

create table ABC (text varchar2(10), day date);
insert into ABC values('SATDY',sysdate);
insert into ABC values('GIGIOOL',sysdate-1);
insert into ABC values('GOOOL',sysdate-2);
create user X identified by X;
create user Y identified by Y;
grant connect, resource to X;
grant connect, resource to Y;
grant select on ABC to X;
grant select on ABC to Y;

SQL> select * from boss.abc
2 where 'X' = (select username from user_users)
3 union all
4 select * from boss.abc
5 where 'Y' = (select username from user_users);

TEXT DAY
---------- ---------
SATDY 17-DEC-01
GIGIOOL 16-DEC-01
GOOOL 15-DEC-01

Elapsed: 00:00:00.20
SQL>