Difference between Clustered Index and Non Clustered Index

A clustered index is a special type of index that reorders the way records in the table are physically stored.

Therefore table can have only one clustered index and this is usually made on the primary key. The leaf nodes of a clustered index contain the data pages.

A nonclustered 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 disk. The leaf node of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

There can be as many as 249 nonclustered index per table