Shulou(Shulou.com)05/31 Report--

Today, I will talk to you about the reasons that are easy to cause oracle index failure, which may not be well understood by many people. In order to make you understand better, the editor has summarized the following contents for you. I hope you can get something according to this article.

There are many reasons that can easily cause oracle index failures:

1. Use functions on index columns. Such as SUBSTR,DECODE,INSTR, etc., operate on the index column. It can be solved by establishing a functional index.

2. The newly created table has not yet had time to generate statistical information, so it is fine to analyze it.

3. Based on the cost analysis of cost, the table accessed is too small, and the consumption of using full table scan is less than that of using index.

4. Use, not in, not exist, for these three cases, the result set is considered to be very large. Generally, if the result set is greater than 5%, 15%, you will not go to the index but FTS (full table scan).

5. Separate >,

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