正在阅读：Oracle迁移到优化器系列1.1Oracle迁移到优化器系列1.1

2004-02-14 09:34 出处：PConline 作者：mindsware/CSDN 责任编辑：linjixiong

请注意，用以搜索列的操作符也扮演着决定级别的角色，有时甚至考虑索引的时间作为级别

例如下面的表证明了在列1和列2上的索引使用情况,如果它们两个在where子句上用”=”连接

例:

   select * from am79 where col1 = 1 and col2 = 'amar';
-- here both col1 and col2 are indexed.

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Normal index types | Index used in RBO
   column1(a) column2(b)column1+column2(c) |
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non-uniquenon-unique c
non-unique non-unique a + b
non-unique non-uniquenon-unique c
unique non-unique a
unique non-unique a
unique unique b (the most recent index created)
unique uniqueunique c
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  -The above is tested on Oracle 8.1.7.1.
   -In case of non-unique single column indexes, both indexes are used.
   -In case of unique indexes, they are not combined for execution plan, any one is taken.
   -Preference is given to the index available with the "=" operator column, than with
   others operators.
   -Don't create bitmap & function-based indexes, these will not work in RBO.
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