Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quickly.
There are clustered and nonclustered indexes.
A clustered index is a special type of index that reorders the way in which records in the table are physically stored. Therefore tablecan have only one clustered index. 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.
