接着,我们来使用这里的hint push_pred强制优化器将谓词merge进view中,可见到“VIEW PUSHED PREDICATE”: select /*+push_pred(haoview)*/ hao3.object_name from hao3,haoview where hao3.object_name=haoview.object_name(+) and hao3.object_id=999; --- | Id | Operation | Name | Rows | Bytes ...
1、NO_PUSH_PRED 提示是指导优化器不要将连接谓词推入到视图或出现在from子句中的子查询中。 2、当把NO_PUSH_PRED提示写入到内联视图中时,不需要提定目标表名。
可见,对于此种身处outger join右侧的view来说,merge hint已经力所不及了。 综上,对于大师斗劲轻易混合的三个hint: no_unnest/unnest是针对子查询是否展开的,push_subq是针对子查询的连接次序的,push_pred则是针对unmergeable view应用外部查询谓词。 http://www.cnpetweb.com/a/xinxizhongxin/lanmu9/20...
The /*+ push_pred */ hint instructs the Oracle optimizer to push the filter predicates from the outer query block to the inner query block. By pushing the filter predicates, the amount of data sent …
常常有人把这三个hint搞混,主要是因为对三种重写原理不清楚。特总结如下。(实验环境为10204) 1. no_unnest, unnest unnest我们称为对子查询展开,顾名思义,就是别让子查询孤单地嵌套(nest)在里面。 所以un_unnest双重否定代表肯定,即让子查询不展开,让它嵌套(nest)在里面。
上面的例子中,oracle自动将子查询进行了展开,下面我们使用no_unnest hint来不让oracle在这里进行子查询展开,就通过 嵌套在子查询里面,那么这样比如就会走fiter了,如下: SQL> alter system flush shared_pool; System altered. SQL> select object_id 2 from t1 ...
Oracle联合查询 2019-12-05 14:37 −Oracle联合查询1、union(并集,不显示重复数据) select * from emp1 union select * from emp22、union all(并集,并且显示重复的数据) se... 清欢QQ 0 3517 IDEA从Github中pull或者push成功之后tomcat启动不了,报Error... 2019...
• Push_pred / no_push_pred: If you have a non-mergeable view (possible because of a no_merge hint) in your query, how should you operate the join from other tables; should you create one large view result and join it once (no_push_pred) or should you push the join predicate ...
加上hint后,SQL会在1秒以内完成。 3.push_pred 在谈到push_pred这个hint时,首先要搞清楚mergeable view和unmergeable view的区别。 这个在concept上有明确解释: Mergeable and Unmergeable ViewsThe optimizer can merge a view into a referencing query block when the view has one or more base tables, prov...
【转】CBO hint:no_unnest,push_subq,push_pred的用法 原博客地址:http://blog.itpub.net/15415488/viewspace-663969 常常有人把这三个hint搞混,主要是因为对三种重写原理不清楚。特总结如下。(实验环境为10204) 1. no_unnest, unnest unnest我们称为对子查询展开,顾名思义,就是别让子查询孤单地嵌套(nest)...