What are indexes in databases and what are they for? How do they work?

Database indexes are special data structures that speed up the search and retrieval of data from tables. They work like pointers or directories, allowing quick access to the needed records without scanning all rows.

How indexes work:

• An index is created on one or more columns of a table.
• Inside, the index is usually implemented using balanced trees (such as B-trees) or hash tables.
• When executing a query with a condition on an indexed column, the DBMS refers to the index to quickly find the addresses of the required rows.
• This significantly reduces query execution time, especially with large volumes of data.

Indexes are useful for speeding up SELECT operations but can slow down INSERT, UPDATE, DELETE operations, as the index needs to be updated. Therefore, it is important to create indexes consciously, based on frequent queries and search conditions.