In a clustered index, the leaf level of the index is the actual data page. Data is physically stored in a clustered index is ascending order. A table can only have one clustered index. Similar to a table scan, this is when the Query Optimizer reads each record in a clustered index to locate one or more records. Refers to Transact-SQL code used to create, alter, or drop database objects.
Density is also related to selectivity .
Low selectivity is related to high density, and high selectivity is related to low density. Since each page in SQL Server holds 8K, an extend is 64K in size. There are mixed and uniform extents found in SQL Server versions 7.0 and 2000. A mixed extent contains pages from two or more objects. Uniform extents have all of their 8 pages allocated to the same object.