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An Index is a key built from one or more columns in the database that speeds up fetching rows from the table or view.


sorts the data rows in the table on their key values.


stores the data at one location and indices at another location.

Parameters Clustered Non-clustered
Use for You can sort the records and store clustered index physically in memory as per the order. A non-clustered index helps you to creates a logical order for data rows and uses pointers for physical data files.
Storing method Allows you to stores data pages in the leaf nodes of the index. This indexing method never stores data pages in the leaf nodes of the index.
Size The size of the clustered index is quite large. The size of the non-clustered index is small compared to the clustered index.
Data accessing Faster Slower compared to the clustered index
Additional disk space Not Required Required to store the index separately
Type of key By Default Primary Keys Of The Table is a Clustered Index. It can be used with unique constraint on the table which acts as a composite key.
Main feature A clustered index can improve the performance of data retrieval. It should be created on columns which are used in joins.


  • Dense Index
  • Sparse Index



B-Tree Index