What are the common types of database indexes used to enhance data retrieval speed?

Database indexes are primarily used to enhance data retrieval speed. The common types of database indexes include: 1. B-Tree: This is the most common type of index that organizes data in a balanced tree structure, allowing for efficient searching and retrieval based on key values. 2. Hash: This type of index uses a hash function to map keys to their corresponding values, offering fast access to data but is limited to equality searches. 3. Bitmap: Bitmap indexes store bitmaps for each distinct value in a column, making them efficient for low cardinality columns but less suitable for high cardinality data. 4. Clustered: This type of index reorders the way records are physically stored on disk to match the index order, reducing disk I/O and improving query performance.