Indexes in SQL | Clustered and Non Clustered Index

Indexes in SQL are data structures that optimize the speed of data retrieval operations from database tables. They allow the database engine to quickly locate data, similar to an index in a book. However, indexes can introduce overhead for write operations because they must also be updated whenever the data changes. There are two types of indexes in SQL: clustered and non-clustered. A clustered index determines the physical order of data in a table and can only be created once per table. A non-clustered index creates a separate structure that maintains a pointer to the physical data in the table and can be created multiple times on a single table. Clustered indexes are efficient for range queries and faster retrieval for queries filtering on the clustered index column. Non-clustered indexes improve performance for queries on non-primary key columns and allow multiple indexes for various query optimizations. Use a clustered index when retrieving data based on the order of a key, and use a non-clustered index when frequently querying other columns to enhance retrieval performance. Indexes can significantly enhance the performance of database queries, making them an essential tool for database management.