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发布时间:2016-11-07 18:07:46

语法: { CONNECT BY [ NOCYCLE ] condition [ START WITH condition ]| START WITH condition CONNECT BY [ NOCYCLE ] condition}START WITH:specifies the root row(s) of the hierarchy.CONNECT BY:specifies the relationship between parent rows and child rows of the hierarchy.  1.In a hierarchi.........【阅读全文】

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发布时间:2016-08-06 16:40:53

昨天一条sql造成了大量的CBC latch等待,CPU超过了90%,sql每次执行消耗了6441854逻辑读,耗时130s,只返回3行,基本全部消耗在CPU上,sql文本以及执行计划如下:sql文本SELECT /*+qb_name(a)*/ t.idFROM venustech.venus_acc_organizationview t start WITH t.id IN (? ? ? ? SELECT /*+qb_.........【阅读全文】

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发布时间:2016-08-05 18:51:40

   对于递归查询,在11g之前只能用start with ... connnect by prior来实现,11g之后可用with as来实现,这里的讨论只基于connect by的形式。 ----------------------------------- ---------- ------------------------------------------------------------ _optimizer_connect_by_combine_sw    T.........【阅读全文】

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发布时间:2016-07-21 11:45:38

1.定义: The purpose of subquery coalescing is to combine equivalent semi- and anti-join subqueries into a single query block. The main reason for applying this heuristic-based query transformation, which is available as of version 11.2, is to reduce the number of table accesses, and thus to redu.........【阅读全文】

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发布时间:2016-07-19 14:27:27

1.定义 The purpose of join elimination is to remove redundant joins—in other words, to completely avoid executing a join even if a SQL statement explicitly calls for it. The key information used by the query optimizer to decide whether it’s sensible to implement this query transformation is th.........【阅读全文】

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给主人留下些什么吧!~~

gydba2016-09-21 14:38

大神啊,求指教!

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