Dav*_*542 9 sql sql-server oracle postgresql materialized-views
这与我问的上一个问题有关，带有时间戳表达式的 Saved View，关于在（非物化）视图中存储信息。当用户执行以下操作时，数据将如何存储和检索：
CREATED MATERIALIZED VIEW mv AS SELECT person_id, name, NOW() as now FROM table
# is this more-or-less the same as:
# CREATED TABLE tb AS SELECT person_id, name, NOW() as now FROM table
# "AND UPDATE EVERY..."
NOW()表达式是否作为值保存到存储中，或者是否在查询时为物化视图评估了任何函数？物化视图是否与表相同，它在存储级别进行了某种优化/刷新，还是我错过了这条船？
这里的这篇文章表明（至少从功能上讲）可以将物化视图模拟为带有触发器的表：https : //www.materialized.info/。
这将取决于您使用的数据库平台。看到你用“oracle”标记了这个，这就是 Oracle 中发生的事情。
“now”值（在本例中为“sysdate”）在物化视图实例化时进行评估。这很容易证明
SQL> create materialized view MV as select e.*, sysdate d from emp e;
Materialized view created.
SQL> select * from mv;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO D
---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- -------------------
7369 SMITH CLERK 7902 17/12/1980 00:00:00 800 20 21/10/2020 12:18:26
7499 ALLEN SALESMAN 7698 20/02/1981 00:00:00 1600 300 30 21/10/2020 12:18:26
7521 WARD SALESMAN 7698 22/02/1981 00:00:00 1250 500 30 21/10/2020 12:18:26
7566 JONES MANAGER 7839 02/04/1981 00:00:00 2975 20 21/10/2020 12:18:26
7654 MARTIN SALESMAN 7698 28/09/1981 00:00:00 1250 1400 30 21/10/2020 12:18:26
7698 BLAKE MANAGER 7839 01/05/1981 00:00:00 2850 30 21/10/2020 12:18:26
7782 CLARK MANAGER 7839 09/06/1981 00:00:00 2450 10 21/10/2020 12:18:26
7788 SCOTT ANALYST 7566 09/12/1982 00:00:00 3000 20 21/10/2020 12:18:26
7839 KING PRESIDENT 17/11/1981 00:00:00 5000 10 21/10/2020 12:18:26
7844 TURNER SALESMAN 7698 08/09/1981 00:00:00 1500 30 21/10/2020 12:18:26
7876 ADAMS CLERK 7788 12/01/1983 00:00:00 1100 20 21/10/2020 12:18:26
7900 JAMES CLERK 7698 03/12/1981 00:00:00 950 30 21/10/2020 12:18:26
7902 FORD ANALYST 7566 03/12/1981 00:00:00 3000 20 21/10/2020 12:18:26
7934 MILLER CLERK 7782 23/01/1982 00:00:00 1300 10 21/10/2020 12:18:26
[wait 10 seconds]
14 rows selected.
SQL> select * from mv;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO D
---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- -------------------
7369 SMITH CLERK 7902 17/12/1980 00:00:00 800 20 21/10/2020 12:18:26
7499 ALLEN SALESMAN 7698 20/02/1981 00:00:00 1600 300 30 21/10/2020 12:18:26
7521 WARD SALESMAN 7698 22/02/1981 00:00:00 1250 500 30 21/10/2020 12:18:26
7566 JONES MANAGER 7839 02/04/1981 00:00:00 2975 20 21/10/2020 12:18:26
7654 MARTIN SALESMAN 7698 28/09/1981 00:00:00 1250 1400 30 21/10/2020 12:18:26
7698 BLAKE MANAGER 7839 01/05/1981 00:00:00 2850 30 21/10/2020 12:18:26
7782 CLARK MANAGER 7839 09/06/1981 00:00:00 2450 10 21/10/2020 12:18:26
7788 SCOTT ANALYST 7566 09/12/1982 00:00:00 3000 20 21/10/2020 12:18:26
7839 KING PRESIDENT 17/11/1981 00:00:00 5000 10 21/10/2020 12:18:26
7844 TURNER SALESMAN 7698 08/09/1981 00:00:00 1500 30 21/10/2020 12:18:26
7876 ADAMS CLERK 7788 12/01/1983 00:00:00 1100 20 21/10/2020 12:18:26
7900 JAMES CLERK 7698 03/12/1981 00:00:00 950 30 21/10/2020 12:18:26
7902 FORD ANALYST 7566 03/12/1981 00:00:00 3000 20 21/10/2020 12:18:26
7934 MILLER CLERK 7782 23/01/1982 00:00:00 1300 10 21/10/2020 12:18:26
14 rows selected.
无论您查询物化视图的次数如何，“D”列都保持不变。如果我现在为物化视图发出刷新命令，我们实际上是在重新运行定义查询，因此 sysdate（因此列“D”）将被选择作为刷新的时刻。
SQL> exec dbms_mview.refresh('MV')
PL/SQL procedure successfully completed.
SQL> select * from mv;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO D
---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- -------------------
7369 SMITH CLERK 7902 17/12/1980 00:00:00 800 20 21/10/2020 12:19:12
7499 ALLEN SALESMAN 7698 20/02/1981 00:00:00 1600 300 30 21/10/2020 12:19:12
7521 WARD SALESMAN 7698 22/02/1981 00:00:00 1250 500 30 21/10/2020 12:19:12
7566 JONES MANAGER 7839 02/04/1981 00:00:00 2975 20 21/10/2020 12:19:12
7654 MARTIN SALESMAN 7698 28/09/1981 00:00:00 1250 1400 30 21/10/2020 12:19:12
7698 BLAKE MANAGER 7839 01/05/1981 00:00:00 2850 30 21/10/2020 12:19:12
7782 CLARK MANAGER 7839 09/06/1981 00:00:00 2450 10 21/10/2020 12:19:12
7788 SCOTT ANALYST 7566 09/12/1982 00:00:00 3000 20 21/10/2020 12:19:12
7839 KING PRESIDENT 17/11/1981 00:00:00 5000 10 21/10/2020 12:19:12
7844 TURNER SALESMAN 7698 08/09/1981 00:00:00 1500 30 21/10/2020 12:19:12
7876 ADAMS CLERK 7788 12/01/1983 00:00:00 1100 20 21/10/2020 12:19:12
7900 JAMES CLERK 7698 03/12/1981 00:00:00 950 30 21/10/2020 12:19:12
7902 FORD ANALYST 7566 03/12/1981 00:00:00 3000 20 21/10/2020 12:19:12
7934 MILLER CLERK 7782 23/01/1982 00:00:00 1300 10 21/10/2020 12:19:12
14 rows selected.
SQL>
但每个平台可能都有自己的特点。
此处介绍了 Oracle 物化视图的处理，包括定义和物化视图日志
物化视图的一些更高级的主题（分区、索引等）以及它们如何与自动查询重写相关，这里是