What is the difference between a clustered index and a non-clustered index in SQL Server?

Clustered Index vs. Non-Clustered Index in SQL Server

In SQL Server, clustered and non-clustered indexes are two types of indexes used to improve query performance. Below are the key differences between them:

Clustered Index:

• A clustered index determines the physical order of data in a table.
• Each table can have only one clustered index.
• Data in a clustered index is stored in the same order as the index, making it faster for range queries and queries that return a range of values.
• Using a clustered index is recommended for columns that are frequently used in queries for sorting and range operations.

Non-Clustered Index:

• In a non-clustered index, the physical order of data in the table is independent of the index order.
• A table can have multiple non-clustered indexes.
• Data in a non-clustered index is stored separately from the main table data, usually in a separate data structure.
• Non-clustered indexes are useful for improving the performance of queries that involve columns not specified in the clustered index or for covering queries.

It's important to choose the right type of index based on your query patterns and use cases to optimize performance in SQL Server.