oracle does not use index

Oracle is a commonly used relational database management system used to store, maintain and access large amounts of data. When using Oracle database, we may encounter a problem: the query statement does not use the correct index, causing the query speed to slow down. This article will introduce the reasons and solutions for Oracle not to index.

1. Brief description of Oracle index

The index is a data structure used in the database to improve the query speed, similar to the bibliographic card in the library. It is a data structure created in a database table that speeds up queries. An index can be thought of as a mapping table, where each record in the table contains a pointer to data that points to a row in the table. When the query statement contains index columns or joint index columns, Oracle can use the index data structure to determine the range of data that needs to be queried, thereby improving query efficiency.

2. The reason why Oracle does not use the index

However, in the actual use of the Oracle database, we may find that although some query statements have indexes, the query does not use the index, resulting in query Efficiency slows down. The reasons for this situation may be as follows:

1. Inaccurate query conditions

Inaccurate query conditions are the main reason why query statements are not indexed one. For example, when querying records in a table, if the query conditions include fields that are not indexed in the table, Oracle cannot use the index to speed up the query, resulting in a decrease in query efficiency.

2. Index failure or damage

Index failure or damage is also one of the reasons why the query statement does not go through the index. When the query conditions are inconsistent with the data type or length when creating the index, Oracle cannot use the index for query. In addition, if the index is damaged or deleted, the query statement will not go through the index.

3. Inaccurate database statistics

Oracle helps optimize queries by collecting database statistics. If the statistics are inaccurate or not updated in a timely manner, the query statement will The execution plan does not match the actual situation, resulting in the query statement not going through the index.

3. How to solve the problem of Oracle not indexing

For the problem of Oracle not indexing, we can adopt the following solutions:

1. Regular maintenance Index

Regular maintenance of the index is one of the important measures to ensure the normal operation of the Oracle database. The index can be maintained by checking whether the index is valid, whether the index is damaged, the storage space and performance of the index, etc. For invalid indexes, they need to be rebuilt or deleted and rebuilt to ensure the validity and normal use of the index.

2. Update database statistics

Updating database statistics is another important measure to ensure the normal operation of the Oracle database. Can help optimize queries by collecting and updating database statistics. In Oracle, you can use the relevant procedures in the "DBMS_STATS" package to collect and update database statistics to ensure that the execution plan is consistent with the actual situation.

3. Optimizing query statements

Optimizing query statements is an important way to avoid Oracle not using the index. Query statements can be optimized by optimizing query conditions, checking whether the query statement is consistent with the index data type and length, and avoiding the use of function operations to ensure that Oracle can use the index for querying.

4. Increase index

Increasing index is also a way to improve Oracle query efficiency. You can speed up queries by adding indexes. When creating an index, you need to choose an appropriate index type to ensure the correctness and effectiveness of the index.

In short, Oracle not indexing is a common problem, which may seriously affect the query efficiency and performance of the database. Therefore, we need to regularly maintain indexes and update database statistics to ensure the normal operation of the database. In addition, we need to pay attention to optimizing query conditions when writing query statements to ensure that Oracle can use the index for querying.

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