在9i以前，很多功能都是不區分表和物化視圖的區別的，到了10g以后。很多功能會將表和物化視圖區分對待。
原本通用的COMMENT ON TABLE語句，對物化視圖不再有效，必須要使用COMMENT ON MATERIALIZED VIEW語句代替。
SQL> SELECT * FROM V$VERSION;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
SQL> CREATE TABLE T_BASE (tbID NUMBER, TYPE VARCHAR2(30), NUM NUMBER);
Table created.
SQL> CREATE MATERIALIZED VIEW LOG ON T_BASE
2 WITH ROWID, SEQUENCE (TYPE, NUM)
3 INCLUDING NEW VALUES;
Materialized view log created.
SQL> CREATE MATERIALIZED VIEW MV_BASE
2 REFRESH FAST ENABLE QUERY REWRITE AS
3 SELECT TYPE, SUM(NUM) SUM_NUM, COUNT(NUM) CNT_NUM, COUNT(*) CNT
4 FROM T_BASE
5 GROUP BY TYPE;
Materialized view created.
SQL> COMMENT ON TABLE MV_BASE IS 'COMMENT ON A MATERIALIZED VIEW ';
COMMENT ON TABLE MV_BASE IS 'COMMENT ON A MATERIALIZED VIEW '
*
ERROR at line 1:
ORA-12098: cannot comment on the materialized view
SQL> COMMENT ON MATERIALIZED VIEW MV_BASE IS 'COMMENT ON A MATERIALIZED VIEW ';
Comment created.
SQL> COL COMMENTS FOR A60
SQL> SELECT * FROM USER_MVIEW_COMMENTS;
MVIEW_NAME COMMENTS
------------------------------ ------------------------------------------------------------
MV_BASE COMMENT ON A MATERIALIZED VIEW
其實不只是COMMENT發生了變化，關于物化視圖的執行計劃Oracle也對其進行細化，將物化視圖的掃描和全表掃描區分開：
SQL> SET AUTOT ON EXP
SQL> SELECT COUNT(*) FROM MV_BASE;
COUNT(*)
----------
0
Execution Plan
----------------------------------------------------------
Plan hash value: 3034976462
-------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
-------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | MAT_VIEW ACCESS FULL| MV_BASE | 1 | 2 (0)| 00:00:01 |
-------------------------------------------------------------------------
Note
-----
- dynamic sampling used for this statement
SQL> SELECT /*+ REWRITE */ TYPE, COUNT(*) FROM T_BASE GROUP BY TYPE;
no rows selected
Execution Plan
----------------------------------------------------------
Plan hash value: 1008429399
----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 30 | 2 (0)| 00:00:01 |
| 1 | MAT_VIEW REWRITE ACCESS FULL| MV_BASE | 1 | 30 | 2 (0)| 00:00:01 |
----------------------------------------------------------------------------------------
Note
-----
- dynamic sampling used for this statement
在9i以前，很難從執行計劃中區分掃描的是表還是物化視圖，但是現在一目了然了。
總的來說，這種改進還是很有意義的，用戶可以更清楚的了解處理的對象到底是表還是物化視圖。