《基于ORACLE SQL优化》读书笔记

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注：为读《基于ORACLE SQL优化笔记》

对比RBO 与CBO 在数据选择性不佳的情况下，对执行路径的选择。

select * from emp where mgr = 7902;

1. 骗下优化器，修改表和索引统计信息

2. CBO 对上面语句选择FULLTABLE SCAN;

3. RBO还是走索引。

数据准备：

CREATE TABLE EMP(EMPNO NUMBER(4) NOT NULL,ENAMEVARCHAR2(10),JOB VARCHAR2(9),MGR NUMBER(4),HIREDATE DATE,SAL NUMBER(7, 2),COMMNUMBER(7, 2),DEPTNO NUMBER(2));INSERT INTO EMP VALUES(7369, 'SMITH', 'CLERK',7902,TO_DATE('17-DEC-1980', 'DD-MON-YYYY'), 800, NULL, 20);INSERT INTO EMP VALUES(7499, 'ALLEN', 'SALESMAN',7698,TO_DATE('20-FEB-1981', 'DD-MON-YYYY'), 1600, 300, 30);INSERT INTO EMP VALUES(7521, 'WARD', 'SALESMAN',7698,TO_DATE('22-FEB-1981', 'DD-MON-YYYY'), 1250, 500, 30);INSERT INTO EMP VALUES(7566, 'JONES', 'MANAGER',7839,TO_DATE('2-APR-1981', 'DD-MON-YYYY'), 2975, NULL, 20);INSERT INTO EMP VALUES(7654, 'MARTIN', 'SALESMAN',7698,TO_DATE('28-SEP-1981', 'DD-MON-YYYY'), 1250, 1400, 30);INSERT INTO EMP VALUES(7698, 'BLAKE', 'MANAGER',7839,TO_DATE('1-MAY-1981', 'DD-MON-YYYY'), 2850, NULL, 30);INSERT INTO EMP VALUES(7782, 'CLARK', 'MANAGER',7839,TO_DATE('9-JUN-1981', 'DD-MON-YYYY'), 2450, NULL, 10);INSERT INTO EMP VALUES(7788, 'SCOTT', 'ANALYST',7566,TO_DATE('09-DEC-1982', 'DD-MON-YYYY'), 3000, NULL, 20);INSERT INTO EMP VALUES(7839, 'KING', 'PRESIDENT',NULL,TO_DATE('17-NOV-1981', 'DD-MON-YYYY'), 5000, NULL, 10);COMMIT;ALTER TABLE EMP MODIFY (MGR NOT NULL);CREATE INDEX IDX_EMP_MGR ON EMP(MGR);set  autotrace on

--修改表统计信息

EXEC dbms_stats.set_table_stats(ownname=>'tester',tabname=>'EMP',numrows =>1000000,no_invalidate =>false);

--修改索引统计信息

EXEC dbms_stats.set_index_stats(ownname=>'tester',indname=>'IDX_EMP_MGR',numlblks =>100000,no_invalidate=>false);

--默认CBO:

select * from emp where mgr = 7902;

--当前 SESSION 改为RBO：

Alter session set optimizer_mode =rule;select * from emp where mgr = 7902;

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