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查询计划中集的势（Cardinality）的计算
当使用CBO模式的优化器时，oracle在生成查询计划时，会计算各个访问路径的代价，选择代价最小的访问路径作为查询计划。这个选择过程我们可以通过做一个10053的trace来观察。在做代价估算时，有一个很...
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EXISTS, NOT EXISTS, IN, and NOT IN
Optimizing SQL usually gives the most significant results when DBAs are called upon to “make the system run faster.” Using tools like Statspack or Enterprise Manager, it is often easy to find the ...
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Managing Optimizer Statistics Paper
Over the past couple days I’ve been reading through the recent paper by Karen Morton entitled “Managing Statistics for Optimal Query Performance“. In this paper Karen goes over many of the top...
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Null-Aware Anti-Join
[0006] A common type of query that is optimized is a query that contains a subquery whose join condition involves the NOT IN/ALL operator (NOT IN is equivalent to != ALL). In data-warehouses with ...
