/*
FAST Simple Random Sample from a source table using pseudo random number generator RAND() 

Usage:
Sample Size is set following the "select top" 

Copy and paste more random value subqueries than the sample size
	If the sample size is more than 20% of the source table size, you may have to include many time the sample size of random value subqueries	
	and if more than 50%, consider changing the query to exlude the random rows.

Modify the @SourceRowCount and the first part of the query for your source table name (dbo.phrases in this example)

A random seed is used, but a fixed one can be used if desired
	
	
Advantages:
	Does not use NEWID for randomness, which is not technically a Random Number Genrator
	Is FAST, even when the source table is large Select 10 from 10 million in 6 seconds, 1000 in 8 seconds
	Does not rely on data page assumptions (see TABLESAMPLE)
	
	
Disadvantages:
	Not TRUE random numbers
	
	
See Also:
http://msdn.microsoft.com/en-us/library/aa175776(SQL.80).aspx 
Presents three methods for random samples
		1) Cursors and RAND()   Cursor Overhead
		2) Rand( ROW ID)        Bad randomness
		3) NewID        


http://msdn.microsoft.com/en-us/library/ms189108.aspx
Documentation for TABLESAMPLE		
		1) Can only be used on true tables, not linked, views, XML, etc
		2) Samples pages, not rows, if pages contain correlated row its no longer a simple random sample		        

*/


/*
Find the number of rows in the source table
*/
declare @SourceRowCount integer
select @SourceRowCount=COUNT(*) from dbo.phrases


/*
Initialize the random number generator with a random seed (or a particular seed)
*/
declare @d integer
set @d=RAND()      --set @d=RAND(an integer)


/*
Create Source table from the desired table and ROW_NUMBER()
Join Source to a table of random values between
Select top n from a slightly larger set
*/

select * from
     (select *, ROW_NUMBER() over(order by GETDATE()) as Row from dbo.phrases) 
as source,
(select top 10 n from
(select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n union all
select convert(integer, RAND()*@SourceRowCount) as n) 
as tmp)
as R where source.Row=R.n