When it comes to the SQL server, indexes play a vital role. An index helps in improving the overall performance and the data retrieval timing. You can understand the actual importance of index by an example from the textbook. The textbook includes an index, and through that index, the process of finding the chapter and page number becomes easier. Here in SQL also, the index makes the whole process smooth, fast, and easy.
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In index, keys are cached in a structure that allows SQL Server to attain rows connected with the key values swiftly and efficiently. In general, if the primary key and unique constraint are marked on the table, then the index gets generated automatically.
Index gets automatically generated if the primary key and unique constraint are defined on the table. Two types of indexes: Clustered and Non-clustered indexes. Let’s analyze the difference between Clustered and Non-clustered indexes
What is a Clustered Index?
In SQL Server, the primary key constraint automatically builds a clustered index on a column. According to the protocol, there will be only one clustered index per table. A clustered index is used to define the order or to sort the table or arrange the data by alphabetical order just like a dictionary.
What is a Non Clustered Index?
A non-clustered index collects the data at one place and records at another place. The index carries pointers to the position of that data. According to the protocol, a single table can include many non-clustered indexes.
Difference between Clustered and Non-Clustered Index
| S.No | Clustered | Non-clustered |
| 1 | A clustered index is used to define the order or to sort the table or arrange the data by alphabetical order just like a dictionary. | A non-clustered index collects the data at one place and records at another place. |
| 2 | It is faster than a non-clustered index. | It is slower than the clustered index. |
| 3 | It demands less memory to execute the operation. | It demands more memory to execute the operations. |
| 4 | It permits you to save data sheets in the leaf nodes of the index. | It never saves data sheets in the leaf nodes of the index. |
| 5 | A single table can consist of a sole cluster index. | It can consist of multiple non-clustered indexes. |
| 6 | It has the natural ability to store data on the disk. | It does not have the natural strength to store data on the disk. |
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