What are the principles for creating Oracle indexes?

The principle of creating indexes is determined based on the frequency of queries, the selectivity of data, and query performance. Here are some principles for creating indexes:

1. Frequently used queries should have indexes created: If a particular query is frequently executed, creating an index for the columns in that query can improve query performance.
2. Columns with high selectivity should be indexed: Selectivity refers to the ratio between the number of different values in a column and the total number of rows. Columns with high selectivity have a better effect on indexing.
3. Index should be created on foreign key columns: Foreign key columns are typically used to link two tables and are frequently used in queries and join operations. Creating an index on foreign key columns can improve query performance.
4. The data type of a column should be suitable for creating an index: certain data types (such as strings and dates) are more suitable for creating indexes than others.
5. Having too many indexes is not recommended as it can increase storage space and decrease performance when inserting, updating, or deleting data.
6. Unique indexes should be chosen whenever possible: uniqueness ensures data consistency and allows for faster retrieval of the necessary information during queries.
7. Choosing the right column order for indexes can make them more effectively utilized by the database engine.

It is important to note that creating an index is a complex task that requires considering multiple factors. Improper index design could result in decreased query performance or increased storage space usage. Therefore, before creating an index, it is best to conduct thorough analysis and testing.