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Yearly Archives: 2022

CBO and Partial indexing

Posted on November 2, 2022 by Sayan Malakshinov Posted in bug, CBO, oracle, query optimizing, SQL, trace, troubleshooting Leave a comment

Oracle 12c introduced Partial indexing, which works well for simple partitioned tables with literals. However, it has several significant issues:

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Slow index access “COL=:N” where :N is NULL

Posted on October 31, 2022 by Sayan Malakshinov Posted in CBO, curious, Funny, oracle, query optimizing, SQL, troubleshooting Leave a comment

All Oracle specialists know that a predicate X=NULL can never be true and we should use “X is NULL” in such cases. The Oracle optimizer knows about that, so if we create a table like this:

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