SELECT EMP.*
FROM EMP,DEPT
WHERE DEPT.DEPT_ID = EMP.DEPT_ID;

SELECT EMP.*
FROM EMP;

create table emp(emp_id integer not null
                  ,dept_id integer not null)

alter table emp add constraint emp_fk1 foreign key (dept_id) references dept;

SQL> create table dept
  2  (
  3     dept_id integer not null primary key
  4  )
  5  /

Table created.

SQL> create table emp
  2  (
  3     emp_id integer not null primary key
  4   , dept_id integer not null
  5  )
  6  /

Table created.

SQL> alter table emp add foreign key (dept_id) references dept
  2  /

Table altered.

SQL> set autotrace on
SQL>
SQL> select dept.*
  2  from emp,dept
  3  where dept.dept_id = emp.dept_id
  4  /

no rows selected


Execution Plan
----------------------------------------------------------
Plan hash value: 3956160932

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |     1 |    13 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| EMP  |     1 |    13 |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement (level=2)


Statistics
----------------------------------------------------------
        222  recursive calls
          0  db block gets
         47  consistent gets
          0  physical reads
          0  redo size
        335  bytes sent via SQL*Net to client
        508  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          6  sorts (memory)
          0  sorts (disk)
          0  rows processed

SQL>