Index

An index is a disk-based structure linked to a table or view that facilitates quicker row retrieval. A table or view’s table or view’s columns are used to create keys in an index. These keys are kept in a structure (B-tree) that enables SQL Server to quickly and effectively locate the row or rows that correspond to the key values.

CLUSTERED INDEX	NON-CLUSTERED INDEX
A clustered index is faster.	A non-clustered index is slower.
The clustered index requires less memory for operations.	A non-Clustered index requires more memory for operations.
In a clustered index, the clustered index is the main data.	In the Non-Clustered index, the index is the copy of data.
A table can have only one clustered index.	A table can have multiple non-clustered indexes.
The clustered index has the inherent ability to store data on the disk.	A non-Clustered index does not have the inherent ability to store data on the disk.
Clustered index store pointers to block not data.	Non-Clustered index storescontainThe non-Clustered both value and a pointer to the actual row that holds data.
In Clustered index leaf nodes are actual data itself.	In Non-Clustered index leaf nodes are not the actual data itself rather they only contain included columns.
In a Clustered index, Clustered key defines the order of data within a table.	In a Non-Clustered index, the index key defines the order of data within the index.
A Clustered index is a type of index in which table records are physically reordered to match the index.	A Non-Clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on the disk.
The size of The primary clustered index is large.	The size of the non-clustered index is compared relativelyThe composite is smaller.
Primary Keys of the table by default are clustered indexes.	The composite key when used with unique constraints of the table act as the non-clustered index.