本節分三個場景分別介紹Oracle VPD的相關功能。
測試用的資料表使用Oracle的示例Schema Scott中的emp和dept：
```

SCOTT-orcl@DESKTOP-V430TU3>desc emp
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 EMPNO                                     NOT NULL NUMBER(4)
 ENAME                                              VARCHAR2(10)
 JOB                                                VARCHAR2(9)
 MGR                                                NUMBER(4)
 HIREDATE                                           DATE
 SAL                                                NUMBER(7,2)
 COMM                                               NUMBER(7,2)
 DEPTNO                                             NUMBER(2)

SCOTT-orcl@DESKTOP-V430TU3>desc dept
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 DEPTNO                                    NOT NULL NUMBER(2)
 DNAME                                              VARCHAR2(14)
 LOC                                                VARCHAR2(13)

SCOTT-orcl@DESKTOP-V430TU3>set pagesize 100
SCOTT-orcl@DESKTOP-V430TU3>SELECT e.deptno, d.dname, ENAME,  JOB, SAL, COMM
  2   FROM emp e, dept d
  3   WHERE d.deptno = e.deptno;

DEPTNO DNAME          ENAME      JOB              SAL       COMM
---------- -------------- ---------- --------- ---------- ----------
        10 ACCOUNTING     KING       PRESIDENT       5000
        10 ACCOUNTING     CLARK      MANAGER         2450
        10 ACCOUNTING     MILLER     CLERK           1300
        20 RESEARCH       FORD       ANALYST         3000
        20 RESEARCH       SMITH      CLERK            800
        20 RESEARCH       JONES      MANAGER         2975
        30 SALES          JAMES      CLERK            950
        30 SALES          TURNER     SALESMAN        1500          0
        30 SALES          MARTIN     SALESMAN        1250       1400
        30 SALES          WARD       SALESMAN        1250        500
        30 SALES          ALLEN      SALESMAN        1600        300
        30 SALES          BLAKE      MANAGER         2850

12 rows selected.
```

**過濾允許範圍外的行**
假設我們希望SALES部門只能看到自己部門的資料，不能看到其他部門的資料，按照上一節介紹的內容，可以建立相應的函式，新增相應的訪問策略即可。
*建立函式*
```
SCOTT-orcl@DESKTOP-V430TU3>CREATE OR REPLACE FUNCTION hide_sal_comm (
  2   v_schema IN VARCHAR2,
  3   v_objname IN VARCHAR2)
  4
  5  RETURN VARCHAR2 AS
  6  con VARCHAR2 (200);
  7
  8  BEGIN
  9   con := 'deptno=30';
 10   RETURN (con);
 11  END hide_sal_comm;
 12  /

Function created.
```
*新增策略*
```
SCOTT-orcl@DESKTOP-V430TU3>BEGIN
  2   DBMS_RLS.DROP_POLICY(
  3     object_schema         => 'scott',
  4     object_name           => 'emp',
  5     policy_name           => 'hide_sal_policy');
  6  END;
  7  /
BEGIN
*
ERROR at line 1:
ORA-28102: policy does not exist
ORA-06512: at "SYS.DBMS_RLS", line 59
ORA-06512: at line 2

SCOTT-orcl@DESKTOP-V430TU3>BEGIN
  2   DBMS_RLS.ADD_POLICY(
  3     object_schema         => 'scott',
  4     object_name           => 'emp',
  5     policy_name           => 'hide_sal_policy',
  6     policy_function       => 'hide_sal_comm');
  7  END;
  8  /

PL/SQL procedure successfully completed.

```
*查詢驗證*
```
SCOTT-orcl@DESKTOP-V430TU3>SELECT e.deptno, d.dname, ENAME,  JOB, SAL, COMM
  2   FROM emp e, dept d
  3   WHERE d.deptno = e.deptno;

DEPTNO DNAME          ENAME      JOB              SAL       COMM
---------- -------------- ---------- --------- ---------- ----------
        30 SALES          ALLEN      SALESMAN        1600        300
        30 SALES          WARD       SALESMAN        1250        500
        30 SALES          MARTIN     SALESMAN        1250       1400
        30 SALES          BLAKE      MANAGER         2850
        30 SALES          TURNER     SALESMAN        1500          0
        30 SALES          JAMES      CLERK            950

6 rows selected.
```
返回的資料均為SALES部門中的資料。

**涉及到敏感列時，過濾允許範圍外的行**
假設這一次我們希望在查詢某些敏感列時才過濾，而不查詢這些列時就不過濾。VPD透過在新增策略時指定sec_relevant_cols實現。
*新增策略*
```
SCOTT-orcl@DESKTOP-V430TU3>BEGIN
  2   DBMS_RLS.DROP_POLICY(
  3     object_schema         => 'scott',
  4     object_name           => 'emp',
  5     policy_name           => 'hide_sal_policy');
  6  END;
  7  /

PL/SQL procedure successfully completed.

SCOTT-orcl@DESKTOP-V430TU3>
SCOTT-orcl@DESKTOP-V430TU3>
SCOTT-orcl@DESKTOP-V430TU3>BEGIN
  2   DBMS_RLS.ADD_POLICY(
  3     object_schema         => 'scott',
  4     object_name           => 'emp',
  5     policy_name           => 'hide_sal_policy',
  6     policy_function       => 'hide_sal_comm',
  7     sec_relevant_cols     =>' sal,comm');
  8  END;
  9  /

PL/SQL procedure successfully completed.

SCOTT-orcl@DESKTOP-V430TU3>
```

*查詢驗證*
```
-- 不涉及敏感列
SCOTT-orcl@DESKTOP-V430TU3>SELECT e.deptno,ENAME, d.dname, JOB
  2   FROM emp e, dept d
  3   WHERE d.deptno = e.deptno;

DEPTNO ENAME      DNAME          JOB
---------- ---------- -------------- ---------
        10 KING       ACCOUNTING     PRESIDENT
        10 CLARK      ACCOUNTING     MANAGER
        10 MILLER     ACCOUNTING     CLERK
        20 FORD       RESEARCH       ANALYST
        20 SMITH      RESEARCH       CLERK
        20 JONES      RESEARCH       MANAGER
        30 JAMES      SALES          CLERK
        30 TURNER     SALES          SALESMAN
        30 MARTIN     SALES          SALESMAN
        30 WARD       SALES          SALESMAN
        30 ALLEN      SALES          SALESMAN
        30 BLAKE      SALES          MANAGER

12 rows selected.

-- 涉及敏感列
  1  SELECT e.deptno, d.dname, ENAME,  JOB, SAL, COMM
  2     FROM emp e, dept d
  3*    WHERE d.deptno = e.deptno
SCOTT-orcl@DESKTOP-V430TU3>/

DEPTNO DNAME          ENAME      JOB              SAL       COMM
---------- -------------- ---------- --------- ---------- ----------
        30 SALES          ALLEN      SALESMAN        1600        300
        30 SALES          WARD       SALESMAN        1250        500
        30 SALES          MARTIN     SALESMAN        1250       1400
        30 SALES          BLAKE      MANAGER         2850
        30 SALES          TURNER     SALESMAN        1500          0
        30 SALES          JAMES      CLERK            950

6 rows selected.
```
不涉及敏感列時，返回所有行，而涉及敏感列時，則返回可訪問範圍內的行，過濾範圍外的行。

**涉及到敏感列資料時，脫敏敏感資料**
最後，假設我們希望在查詢某些敏感列時不過濾，但不能顯示資料，而只能輸出NULL。VPD透過在新增策略時指定sec_relevant_cols和sec_relevant_cols_opt實現。
*新增策略*
```
SCOTT-orcl@DESKTOP-V430TU3>BEGIN
  2   DBMS_RLS.DROP_POLICY(
  3     object_schema         => 'scott',
  4     object_name           => 'emp',
  5     policy_name           => 'hide_sal_policy');
  6  END;
  7  /

PL/SQL procedure successfully completed.

SCOTT-orcl@DESKTOP-V430TU3>
SCOTT-orcl@DESKTOP-V430TU3>BEGIN
  2   DBMS_RLS.ADD_POLICY(
  3     object_schema         => 'scott',
  4     object_name           => 'emp',
  5     policy_name           => 'hide_sal_policy',
  6     policy_function       => 'hide_sal_comm',
  7     sec_relevant_cols     =>' sal,comm',
  8     sec_relevant_cols_opt => dbms_rls.ALL_ROWS);
  9  END;
 10  /

PL/SQL procedure successfully completed.

```

*查詢驗證*
```
SCOTT-orcl@DESKTOP-V430TU3>SELECT e.deptno,ENAME, d.dname, JOB, SAL, COMM
  2   FROM emp e, dept d
  3   WHERE d.deptno = e.deptno;

DEPTNO ENAME      DNAME          JOB              SAL       COMM
---------- ---------- -------------- --------- ---------- ----------
        10 KING       ACCOUNTING     PRESIDENT
        10 CLARK      ACCOUNTING     MANAGER
        10 MILLER     ACCOUNTING     CLERK
        20 FORD       RESEARCH       ANALYST
        20 SMITH      RESEARCH       CLERK
        20 JONES      RESEARCH       MANAGER
        30 JAMES      SALES          CLERK            950
        30 TURNER     SALES          SALESMAN        1500          0
        30 MARTIN     SALES          SALESMAN        1250       1400
        30 WARD       SALES          SALESMAN        1250        500
        30 ALLEN      SALES          SALESMAN        1600        300
        30 BLAKE      SALES          MANAGER         2850

12 rows selected.
```
可以看到，允許範圍內（SALES部門）的行，SAL和COMM都可以正常顯示資料，而範圍外的資料全部為NULL。

**參考資料**
[Using Oracle Virtual Private Database to Control Data Access](https://docs.oracle.com/en/database/oracle/oracle-database/12.2/dbseg/using-oracle-vpd-to-control-data-access.html#GUID-E6343F14-933E-4980-A67A-D5AAEC5743C5)

Oracle vs PostgreSQL DBA（22）- Oracle VPD#2

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