What types of indexes are there in a database and what are they used for?

Indexes in databases are special data structures that speed up searching and sorting data in tables. They are necessary to improve query performance, especially when working with large volumes of data.

Main types of indexes:

• B-Tree index — the most common type, suitable for range searches, sorting, and exact searches.
• Hash index — effective for exact key searches but does not support range queries.
• Full-text index — used for text searches, for example, in search engines.
• Spatial index — for geographic data and queries based on spatial coordinates.
• Composite index — an index on multiple columns, speeds up queries with filtering on several fields.

Indexes reduce the number of disk read operations but increase the time for inserting and updating data, as the index also needs to be updated. Therefore, it is important to choose indexes based on the nature of queries and the load on the database.