网站建设怎么办,深圳代理记账公司前十名,什么是网络营销定价中除免费策略外,网站备案哪个部门odered hint 可以指示oracle 使用from 关键字后面的表的顺序进行join连接#xff01;cbo会优先按照from 后面的表的顺序来进行join#xff0c;当统计leading hint 可以指示Oracle使用leading 中指定的表作为驱动表,比如 正常的访问计划如下SCOTT select e.ename, hiredat…odered hint 可以指示oracle 使用from 关键字后面的表的顺序进行join连接cbo会优先按照from 后面的表的顺序来进行join当统计leading hint 可以指示Oracle使用leading 中指定的表作为驱动表,比如 正常的访问计划如下SCOTT select e.ename, hiredate, b.comm2 from emp e, bonus b3 where e.ename b.ename;Execution Plan----------------------------------------------------------Plan hash value: 1125985041----------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |----------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 34 | 6 (17)| 00:00:01 ||* 1 | HASH JOIN | | 1 | 34 | 6 (17)| 00:00:01 || 2 | TABLE ACCESS FULL| BONUS | 1 | 20 | 2 (0)| 00:00:01 || 3 | TABLE ACCESS FULL| EMP | 14 | 196 | 3 (0)| 00:00:01 |----------------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------1 - access(E.ENAMEB.ENAME)我们在leading 提示中指定 emp 表为驱动表SCOTT select /* leading(e b) */ e.ename,hiredate,b.comm2 from emp e, bonus b3 where e.ename b.ename;Execution Plan----------------------------------------------------------Plan hash value: 1842254584----------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |----------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 34 | 6 (17)| 00:00:01 ||* 1 | HASH JOIN | | 1 | 34 | 6 (17)| 00:00:01 || 2 | TABLE ACCESS FULL| EMP | 14 | 196 | 3 (0)| 00:00:01 || 3 | TABLE ACCESS FULL| BONUS | 1 | 20 | 2 (0)| 00:00:01 |----------------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------1 - access(E.ENAMEB.ENAME)如结果执行计划中将emp 作为驱动表1 在leading 提示同时使用ordered hint则leading hint无效SCOTT select /* leading(b e) ordered */ e.ename,hiredate, b.comm2 from emp e, bonus b3 where e.ename b.ename;Execution Plan----------------------------------------------------------Plan hash value: 1842254584----------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |----------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 34 | 6 (17)| 00:00:01 ||* 1 | HASH JOIN | | 1 | 34 | 6 (17)| 00:00:01 || 2 | TABLE ACCESS FULL| EMP | 14 | 196 | 3 (0)| 00:00:01 || 3 | TABLE ACCESS FULL| BONUS | 1 | 20 | 2 (0)| 00:00:01 |----------------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------1 - access(E.ENAMEB.ENAME)2 使用两个冲突的leading hint 则oracle cbo会忽略所有的leading 提示SCOTT select /* leading(b e) leading(e b) */e.ename,hiredate, b.comm2 from emp e, bonus b3 where e.ename b.ename;Execution Plan----------------------------------------------------------Plan hash value: 1125985041----------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |----------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 34 | 6 (17)| 00:00:01 ||* 1 | HASH JOIN | | 1 | 34 | 6 (17)| 00:00:01 || 2 | TABLE ACCESS FULL| BONUS | 1 | 20 | 2 (0)| 00:00:01 || 3 | TABLE ACCESS FULL| EMP | 14 | 196 | 3 (0)| 00:00:01 |----------------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------1 - access(E.ENAMEB.ENAME)本文原创发布php中文网转载请注明出处感谢您的尊重
