SQL> create or replace view t_view as select * from t where rownum < 11;

View created.

-- this definition is stored in the data dictionary and is used by Oracle when you query against the view

SQL> select view_name,text  from user_views where view_name='T_VIEW';

VIEW_NAME
------------------------------
TEXT
--------------------------------------------------------------------------------
T_VIEW
select "EMPNO","ENAME","JOB","MGR","HIREDATE","SAL","COMM","DEPTNO" from t where
 rownum < 11

SQL> set autotrace on explain

SQL> select ename from t_view ;    

ENAME
----------
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER

10 rows selected.

Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=10 Bytes=70)
   1    0   VIEW OF 'T_VIEW' (Cost=2 Card=10 Bytes=70)
   2    1     COUNT (STOPKEY)
   3    2      <B> TABLE ACCESS (FULL) OF 'T'</B> (Cost=2 Card=14 Bytes=70)

-- as you see ,its the Table T where it gets the data from.

SQL> delete from t_view;
delete from t_view
            *
ERROR at line 1:
ORA-01732: data manipulation operation not legal on this view

-- this is becos we used ROWNUM to restrict to 10 rows and these can be ANY row.

-- now lets be more specific

SQL> create or replace view t_view as select * from t where ename='SMITH';

View created.

SQL> select * from t_view;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM
---------- ---------- --------- ---------- --------- ---------- ----------
    DEPTNO
----------
      7369 SMITH      CLERK           7902 17-DEC-80        800
        20

SQL> delete from t_view;

1 row deleted.

SQL> commit;

Commit complete.

SQL>  select * from t_view;

no rows selected

SQL> select * from t where ename='SMITH';

no rows selected

-- now,lets insert a record into the table through the view

SQL> insert into t_view values(1,'TEST','CLERK',7369,sysdate,900,null,20);

1 row created.

SQL> commit;

Commit complete.

SQL> select * from t_view;

no rows selected

-- the view doesnt return any rows becos the view T_VIEW cant see the record of employee 'TEST', becos its not its definition(ie where ename='SMITH')

SQL> select * from t where ename='TEST';

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM
---------- ---------- --------- ---------- --------- ---------- ----------
    DEPTNO
----------
         1 TEST       CLERK           7369 21-JAN-04        900
        20

-- but the record is there in the table .