What is the Difference Between Clustered and Nonclustered Index?
🆚 Go to Comparative Table 🆚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:
- 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.
- 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.
- Memory requirement: Clustered indexes demand less memory to execute operations, while non-clustered indexes demand more memory to execute operations.
- Access speed: Clustered indexes offer faster data access, while non-clustered indexes are slower.
- 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:
Clustered Index | Non-clustered Index |
---|---|
Defines the order or sorts the table, arranging the data in alphabetical order | Collects data at one place and records at another place, not affecting the table's order |
Faster than non-clustered indexes | Slower than clustered indexes |
Requires less memory to execute operations | Requires more memory to execute operations |
Saves data pages with the leaf nodes of the index | Does not save data pages with the leaf nodes of the index |
A single table can have only one clustered index | A single table can have multiple non-clustered indexes |
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.
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