What types of index structures are applicable in databases and for what purpose are they used?

Different index structures are used in databases to speed up data search and sorting:

• B-trees (B-Tree) — balanced trees widely used for indexing, allowing quick range value searches.
• Hash indexes — use hash functions for fast exact key searches but are not suitable for range queries.
• Bitmap indexes — effective for columns with a small number of unique values, often used in analytical databases.
• R-trees — used for indexing spatial data (geometry, maps).

Indexes reduce query execution time but occupy additional space and require updating when data changes.