oracle does not use index

With the popularity of databases used by major enterprises, the optimization of database indexes has become an essential task. However, in actual database operation and maintenance, we will also encounter some situations where the index cannot be used, such as the problem of not using the index in the Oracle database. This article will explore this issue from the following aspects: Why is there no indexing? How can I find and fix this problem?

1. Reasons for not using the index

When we execute a SQL statement, Oracle will execute the query according to the execution plan corresponding to the SQL statement. In the execution plan, the use of indexes plays a vital role in query performance, which can effectively improve the speed and accuracy of querying data. However, in some cases, we will find that the Oracle database does not use indexes, and in this case, the index may not be used.

The reasons for not using the index usually include the following:

1. Index failure or loss: When the index in the database is reduced, deleted or invalid, the query statement cannot use the index. . This problem usually occurs when the data table structure changes, data is imported or dumped.

2. Uneven data distribution: When the data in the data table is unevenly distributed, the optimization effect of the index on the query statement will be affected. Uneven data distribution usually occurs in some hot data, making the role of the index less obvious.

3. A large amount of duplicate data: When there is a large amount of duplicate data in the data table, the index will lose its effect, resulting in no indexing. This problem usually occurs when the repeated data fields in the data table are not indexed.

4. There are complex query statements: When the SQL statement is too complex, the execution plan will become complicated, which will affect the selection and use of indexes.

2. How to find the problem of not using the index

In actual database operation and maintenance, it is difficult for us to avoid the problem of not using the index, so we need to find and solve this problem. For different problems, we can use different methods to find and solve them.

1. Check whether the index is invalid or lost

When we find that the Oracle database does not use the index, we must first check whether the index is invalid or lost. We can use the GATHER_SCHEMA_STATS function in the dbms_stats package provided by Oracle to view the status of the index, and rebuild and repair the index.

2. Find whether the data distribution is uneven

When the data distribution is uneven, we can use the DBMS_STATS.GATHER_TABLE_STATS function provided by Oracle to update the data distribution and index of the table. At the same time, we can also use Oracle's partitioning function to deal with the uneven distribution of hotspot data.

3. Find whether there is a large amount of duplicate data

When there is a large amount of duplicate data in the data table, we can use advanced functions such as partitioning and reference partition tables provided by Oracle to optimize queries. These advanced functions can help us better manage indexes and data tables and improve query efficiency.

4. Find whether there are complex query statements

When the SQL statement is too complex, we can use the EXPLAIN PLAN function provided by Oracle to view the execution plan and optimize it. At the same time, we can also use Oracle's statistical information analysis to analyze and adjust the execution of SQL statements.

3. Summary and Suggestions

The problem of Oracle database not using indexes is often encountered in actual operation and maintenance. However, we can check the status of the index, data distribution, etc. to find and solve this problem. At the same time, when optimizing database indexes, we should also avoid situations such as uneven data distribution, a large amount of duplicate data, and overly complex SQL statements. We recommend that when using Oracle database, carefully check the status of tables and indexes, and optimize and adjust data tables and SQL statements to ultimately improve query efficiency and performance.

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