**Database Index** is a concept used in databases to quickly locate and access data without processing every row. Database usually creates a **B-Tree** of values being indexed (i.e. selected column that is indexed). It's faster to perform lookup over B-Tree over classic lookup over all rows in database, especially if we have milions of rows. Since index contains pointer to actual row, once there's a match, that row is returned as a result of the query that uses indexes for better performance. **Common Types** - Single Column - Composite - Unique ### See Also - [[Tradeoffs of using Database Index]]