Index

A database index is a data structure (typically a B-tree or hash table) that improves the speed of data retrieval operations on a table at the cost of additional storage space and slower writes. Indexes work similarly to a book index—instead of scanning every page (row) to find information, the database can look up the index to find the exact location. Types include single-column indexes, composite indexes (multiple columns), unique indexes, partial indexes (filtered subsets), and full-text indexes. Proper indexing is one of the most impactful database optimization techniques, potentially reducing query times from minutes to milliseconds.