Doubt in subquery(Is this works properly?)

Question

I have a table USERS
sql>desc users;
Name Null? Type 
USER_ID  NOT NULL  NUMBER(4) 
USERNAME     VARCHAR2(30) 
PASSWORD     VARCHAR2(400) 
ROLE_ID     NUMBER(3) 
EMPLOYEE_ID     NUMBER(4) 
DELETE_STATUS  NOT NULL  VARCHAR2(10) 
PRIVILAGE_USER  NOT NULL  VARCHAR2(50) 
It has no column named as emp_id and I wrongly wrote  a query as
sql>select emp_brc_id
     from employees
     where emp_id =
         (select emp_id
          from users
           where upper(username) = upper('seethalakshman'));
With this query I am expecting an error as: "emp_id" invalid identifier
But it gives o/p( the whole row in employees table in isqlplus.But no o/p in sql developer)
EMP_BRC_ID 
2 
2 
2 
2 
2 
2 
3 
Any explanation pls..                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

Answer 1

Thanks for the reply..
But error is generated if i used any other column name except "EMP_ID"
For eg:
sql>select emp_brc_id    
     from employees    
    where emp_id = (select emp_id1
              from users
              where upper(username) = upper('seethalakshman'));
(select emp_id1
ERROR at line 4:
ORA-00904: "EMP_ID1": invalid identifier