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http://www.sql-server-performance.com/tips/clustered_indexes_p1.aspx
As a rule of thumb, every table should have a clustered index. Generally, but not always, the clustered index should be on a column that monotonically increases--such as an identity column, or some other column where the value is ......
declare @str varchar(50)
declare @i int
set @str = ''
set @i=0
while @i<50
begin
set @str = ......