What are indexes in databases?

Indexes in databases are data structures that speed up the search and retrieval of data from tables. They work similarly to a subject pointer in a book, allowing quick access to needed information without scanning the entire table row by row.

Main types of indexes:

• B-tree: The most common type of index. Suitable for exact searches and range searches.
• Hash: Used for quick lookups based on exact matches. Ineffective for range searches.
• Bitmap: Efficient for columns with a small number of unique values.

Advantages of using indexes:

• Significant acceleration of SELECT query execution.
• Speed up JOIN operations between tables.

Disadvantages of using indexes:

• Take up space on disk.
• Slow down INSERT, UPDATE, DELETE operations, as indexes need to be updated when data changes.
• Require resources for creation and maintenance.

It is important to choose appropriate columns for indexing (often used in WHERE and JOIN clauses) and not to overuse indexes.