What types of indexes exist in database management systems and how are they used to improve query efficiency?

In database management systems (DBMS), there are various types of indexes used to speed up query execution by quickly locating data:

• B-Tree index — the most common type. Used for fast searches, sorting, and range queries. Supports equality and comparison operations.

• Hash index — optimal for equality operations (e.g., WHERE column = value), but does not support range queries.

• Bitmap index — effective for columns with a small number of unique values (low cardinality), often used in analytical databases.

• Full-text index — designed for fast searching of text data, supports searching by words and phrases.

• Spatial index — used for geographic data, such as R-Tree.

Indexes improve query efficiency by reducing the amount of data that needs to be scanned. However, they occupy additional space and slow down insert and update operations, so it is important to choose indexes considering the nature of the queries.