An index can be defined using one or more columns in the table, the index key, with the following restrictions:
You can define an index with up to 16 columns
The maximum size of the index key is 900 bytes
The column(s) defined for the clustered index are referred to as the clustering key. A clustered index is special because it causes SQL Server to order the data in the table according to the clustering key. Because a table cannot be sorted more than one way, you can define only one clustered index on a table.
A table without a clustered index is referred to as a heap. As a general rule of thumb, every table should have a clustered ...