Indexes of SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quicker. Indexes are of two types. Clustered indexes and non-clustered indexes. Rows in the table are stored in the order of the clustered index key.

There can be only one clustered index per table.

Non-clustered indexes have their own storage separate from the table data storage.

Non-clustered indexes are stored as B-tree structures.

Leaf level nodes having the index key and it's row locater

Syntax:

CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name ON table_name