Select n random rows from SQL Server table

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select top 10 percent * from [yourtable] order by newid()
In response to the "pure trash" comment concerning large tables: you could do it like this to improve performance. 

select  * from [yourtable] where [yourPk] in 
(select top 10 percent [yourPk] from [yourtable] order by newid())
The cost of this will be the key scan of values plus the join cost, which on a large table with a small percentage selection should be reasonable.

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