What is the Difference Between Clustered and Nonclustered Index?

The main difference between clustered and non-clustered indexes lies in how they sort and store data in a database table. Here are the key differences between the two:

1. Data organization: A clustered index sorts and stores the data rows in the table based on their key values, while a non-clustered index stores the data at one location and indices at another location.
2. Data storage: Clustered indexes store data pages in the leaf nodes of the index, whereas non-clustered indexes never store data pages in the leaf nodes of the index.
3. Memory requirement: Clustered indexes demand less memory to execute operations, while non-clustered indexes demand more memory to execute operations.
4. Access speed: Clustered indexes offer faster data access, while non-clustered indexes are slower.
5. Indexes per table: A single table can have only one clustered index, while a table can have multiple non-clustered indexes.

In summary, clustered indexes are used to define the order or sort the table and arrange the data by key values, making data retrieval faster. Non-clustered indexes, on the other hand, store data and indices separately, resulting in slower data access.

Comparative Table: Clustered vs Nonclustered Index

The main differences between clustered and non-clustered indexes are as follows:

Here's a brief explanation of each index type:

• Clustered Index: This index sorts and stores the data rows in the table based on their key values. The leaf nodes of a clustered index contain the data pages, and it can only be created when the data or file being moved into secondary memory is in sequential or sorted order.

• Non-clustered Index: This index is a separate object within the same database as the table. Unlike a clustered index, it only contains the index rows, and the logical order of the index does not match the order of the data pages in the leaf nodes. Non-clustered indexes are slower than clustered indexes because they require an additional step to look up the address of the corresponding row in the table.