Oracle foreign key index?

oracle foreign key index, in order to determine whether you need to create an index for the foreign key, you need to consider the following factors: 1. The frequency of query and join operations on the foreign key column. If this is often performed on the foreign key column operations, then it is necessary to create indexes for foreign key columns to improve the performance of these operations; 2. The cardinality of the foreign key column. The cardinality refers to the number of different values ​​in the foreign key column; 3. Foreign key association and The cost of index maintenance, etc. When the data in the table associated with the foreign key changes, the foreign key constraint will automatically check whether the corresponding value exists in the table associated with it.

The operating environment of this tutorial: Windows 10 system, Oracle version 19c, DELL G3 computer.

Oracle foreign key is a constraint used to maintain data integrity. It is used to ensure that when establishing a relationship between two related tables, the value of a column in one table must exist in the associated column of the other table. Foreign key constraints help ensure data consistency and reliability, but the use of indexes in the database is a complex issue. So, before answering the question in the title, we need to understand some concepts related to foreign keys and indexes.

Indices are data structures used to speed up access to data in a database. It allows the database system to quickly find and return rows with a specific value, range, or order. Indexes can reduce database IO overhead and improve query efficiency. In Oracle database, there are many types of indexes, such as B-tree index, bitmap index, hash index, etc.

When designing a database, foreign key constraints are often used together with indexes. The introduction of foreign keys will affect the performance of data insertion, update, and deletion operations. In the absence of foreign keys, these operations only need to operate the data of the source table and the target table. In the case of foreign keys, the integrity of the association conditions also needs to be checked. Such a check process can be very time-consuming, especially if the associated table has a large number of records.

So, do you need to add indexes for foreign keys? The answer is not a simple "yes" or "no", but depends on the specific situation.

First of all, what needs to be considered is the frequency of query and join operations on foreign key columns. If such operations are frequently performed on foreign key columns, it is necessary to create indexes for the foreign key columns to improve the performance of these operations.

Secondly, the cardinality of the foreign key column is an important factor. Cardinality refers to the number of distinct values ​​in the foreign key column. If the cardinality of a foreign key column is low, indexing that column may not result in a significant improvement in performance. However, if the cardinality of the foreign key column is high, it will be very helpful to create an index for this column, because the index can reduce the number of scans of the related table and improve query performance.

In addition, the maintenance cost of foreign key associations and indexes also needs to be considered. When the data in the table associated with the foreign key changes, the foreign key constraint will automatically check whether the corresponding value exists in the associated table. This process may require locking the related tables and performing related index operations when looking up and checking related values. These operations introduce additional overhead, so creating indexes for foreign keys may also incur some maintenance costs.

To summarize, in order to determine whether we need to create an index for a foreign key, we need to consider the following factors: the frequency of query and join operations on the foreign key column, the cardinality of the foreign key column, foreign key associations and indexes Maintenance costs, etc. Creating indexes can improve performance for high-cardinality foreign key columns and columns that are frequently queried and joined. However, for foreign key columns with low cardinality, or when the index maintenance cost is too high during the operation of the database, it may not be necessary to create an index for the foreign key.

When designing the database, we need to comprehensively consider these factors and make decisions about whether to create an index based on the specific situation. This can improve the query and update performance of the database while maintaining data integrity.

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