在Oracle10g中如何使用包DBMS_ADVANCED_REWRITE实现新的查询重写功能

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从Oracle10g版本1开始，提供了新的包DBMS_ADVANCED_REWRITE来实现查询重写。它允许你截获特定的SQL语句，并将
其重定义为另一个SQL语句。下面是一个简单的例子：

1、确认测试用户有必要的权限去运行

CONN sys/password AS SYSDBA

GRANT EXECUTE ON DBMS_ADVANCED_REWRITE TO test;
GRANT CREATE MATERIALIZED VIEW TO test;

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2、创建测试用表

CONN test/test

DROP TABLE rewrite_test_tab;

CREATE TABLE rewrite_test_tab (
id NUMBER,
description VARCHAR2(50),
CONSTRAINT rewrite_test_tab_pk PRIMARY KEY (id)
);

INSERT INTO rewrite_test_tab (id, description) VALUES (1, 'GLASGOW');
INSERT INTO rewrite_test_tab (id, description) VALUES (2, 'BIRMINGHAM');
INSERT INTO rewrite_test_tab (id, description) VALUES (3, 'LONDON');
COMMIT;

EXEC DBMS_STATS.gather_table_stats(USER, 'rewrite_test_tab');

3、查询测试表

SELECT * FROM rewrite_test_tab;

ID DESCRIPTION
---------- --------------------------------------------------
1 GLASGOW
2 BIRMINGHAM
3 LONDON

3 rows selected.

SQL>

4、创建要替换成的SQL使用的视图，然后将上面的语句重定义为查询这个视图

CREATE OR REPLACE VIEW rewrite_test_tab_v AS
SELECT id,
INITCAP(description) AS description
FROM rewrite_test_tab
ORDER BY description;

BEGIN
SYS.DBMS_ADVANCED_REWRITE.declare_rewrite_equivalence (
name => 'test_rewrite',
source_stmt => 'SELECT * FROM rewrite_test_tab',
destination_stmt => 'SELECT * FROM rewrite_test_tab_v',
validate => FALSE,
rewrite_mode => 'TEXT_MATCH');
END;
/

5、初始化参数QUERY_REWRITE_INTEGRITY缺省值为"enforced"，意味只有原始语句的输出和替换后语句的输出完全
一致才会进行重写替换。而我们要实现替换后的输出跟原始输出是有差别的，所以需要将这个参数的值修改为
"TRUSTED"才行。

ALTER SESSION SET QUERY_REWRITE_INTEGRITY = TRUSTED;

Session altered.

SELECT * FROM rewrite_test_tab;

ID DESCRIPTION
---------- --------------------------------------------------
2 Birmingham
1 Glasgow
3 London

3 rows selected.

SQL>

6、视图[USER|ALL|DBA]_REWRITE_EQUIVALENCES中有这些重定义查询的相关信息

SELECT * FROM user_rewrite_equivalences;

OWNER NAME
------------------------------ ------------------------------
SOURCE_STMT
--------------------------------------------------------------------------------
DESTINATION_STMT REWRITE_MO
-------------------------------------------------------------------------------- ----------
TEST TEST_REWRITE
SELECT * FROM rewrite_test_tab
SELECT * FROM rewrite_test_tab_v TEXT_MATCH


1 row selected.

SQL>

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