DEPTNO NOT NULL NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)
TYGER@ORCL>alter table emp
2 add constraint emp_fk_dept
3 foreign key(deptno) references dept(deptno);
Table altered.
TYGER@ORCL>alter table emp modify deptno not null;
Table altered.
TYGER@ORCL>desc emp;
Name Null? Type
----------------------------------------- -------- ----------------------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NOT NULL NUMBER(2)
TYGER@ORCL>set autot traceonly explain
TYGER@ORCL>select count(*) from emp;
COUNT(*)
----------
14
Execution Plan
----------------------------------------------------------
Plan hash value: 155013515
--------------------------------------------------------------------------------
----------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
Time |
--------------------------------------------------------------------------------
----------
| 0 | SELECT STATEMENT | | 1 | 13 | 3 (0)|
00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 13 | |
|
| 2 | MAT_VIEW REWRITE ACCESS FULL| EMP_DEPT | 3 | 39 | 3 (0)|
00:00:01 |
--------------------------------------------------------------------------------
----------
Note
-----
- dynamic sampling used for this statement
可见 当我们将完整性约束全部添加后，优化器有了足够的信息知道这条语句通过物化视图可以查询重写，而不用查询基表，实际的执行情况也印证了这一点。
我们在通过一个例子说明 THUSTED 的情况。我们首先将这些约束去除掉，然后添加一行新的数据
TYGER@ORCL>alter table emp drop constraint emp_fk_dept;
Table altered.
TYGER@ORCL>alter table dept drop constraint dept_pk;
Table altered.
TYGER@ORCL>alter table emp modify deptno null;
Table altered.
TYGER@ORCL>desc dept
----------------------------------------- -------- ----------------------------
DEPTNO NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)
TYGER@ORCL>desc emp;
Name Null? Type
----------------------------------------- -------- ----------------------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)
// 插入一条违反实际约束行
TYGER@ORCL>insert into emp(empno,deptno) values(1,1);
1 row created.
TYGER@ORCL>exec dbms_mview.refresh('EMP_DEPT');
PL/SQL procedure successfully completed.
TYGER@ORCL>alter materialized view emp_dept consider fresh;
alter materialized view emp_dept consider fresh
*
ERROR at line 1:
ORA-30374: materialized view is already fresh
// 创建一个 novalidate 的约束
TYGER@ORCL>alter table dept
2 add constraint dept_pk primary key(deptno)
3 rely enable novalidate
4 /
Table altered.
TYGER@ORCL>alter table emp
2 add constraint emp_fk_dept
3 foreign key(deptno) references dept(deptno)
4 rely enable novalidate
5 /
Table altered.
TYGER@ORCL>alter table emp modify deptno not null novalidate;
Table altered.
回到原来的查询，假如 query_rewrite_integrity = enforced 的话，那么我们知道由于上述约束实际上是违反真实数据约束的，因此优化器将不会利用物化视图查询重写。
TYGER@ORCL>show parameter query
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
query_rewrite_enabled string TRUE
query_rewrite_integrity string enforced
TYGER@ORCL>
TYGER@ORCL>set autot traceonly explain
TYGER@ORCL>select count(*) from emp;
COUNT(*)
----------
16
Execution Plan
----------------------------------------------------------
Plan hash value: 2083865914
-------------------------------------------------------------------
| Id | Operat