Select Random Records From a Table using TableSample in SQL Server 2005/2008

In my previous post, I had explained how to use the NEWID() to Delete Random Records From a Table Using SQL Server 2005/2008

In this post, I will show how to select random records using the TABLESAMPLE clause and use it in different ways. The TABLESAMPLE clause takes a parameter that can be a percent or a sample number representing rows. This clause samples a percentage of
pages randomly. You will get a different result set each time you run a query with the TABLESAMPLE clause. That means that even if you specify to return 50 rows, you will only get an approximate number of rows, that can be less or more than 50 due to the random sampling logic.

Select X% of Records

Returns different set of rows each time the query is executed

USE Northwind


SELECT * FROM Customers


Select X% of Records with same random sampling multiple times

Specify REPEATABLE with seed. REPEATABLE clause returns same set of rows every time that it is executed

USE Northwind


SELECT * FROM Customers



Specify Number of Records instead of %(Percentage)

USE Northwind


SELECT * FROM Customers


Important Points about TABLESAMPLE:

1. If you have upgraded from SQL 2000 to SQL Server 2005, make sure that the compatibility level of the database is set to at least 90.

2. TABLESAMPLE cannot be used on derived tables, OPENXML, Inline Table-Valued functions, linked server tables or a View.

Read more on TABLESAMPLE over here

About The Author

Suprotim Agarwal, MCSD, MCAD, MCDBA, MCSE, is the founder of DotNetCurry, DNC Magazine for Developers, SQLServerCurry and DevCurry. He has also authored a couple of books 51 Recipes using jQuery with ASP.NET Controls and a new one recently at The Absolutely Awesome jQuery CookBook.

Suprotim has received the prestigous Microsoft MVP award for nine times in a row now. In a professional capacity, he is the CEO of A2Z Knowledge Visuals Pvt Ltd, a digital group that represents premium web sites and digital publications comprising of Professional web, windows, mobile and cloud developers, technical managers, and architects.

Get in touch with him on Twitter @suprotimagarwal, LinkedIn or befriend him on Facebook


IGotYourDotnet said...

how can you pull random records out but not duplicate any? Meaning,I have records that can have the same name but different dates or states such as
John Smith 1/2/2010 DE
John Smith 5/14/2008 NJ

how can I only show one name within my random so my users don't get confused?

Madhivanan said...


One possible methods is

select name,min(date) as date from table
tablesample (50 percent)
group by name

Also note that tablesample doesn't work well for small set of data
If all data of table stored in a single page, either it returns all rows or no rows

Run this to understand

city,min(customerid) FROM Northwind..Customers
group by city It returns 69 rows


SELECT city,min(customerid) FROM Northwind..Customers
TABLESAMPLE (50 percent)
group by city

will return all 69 rows or no rows

So better approach is to use top operator with newid()

top 50 percent city,min(customerid) FROM Northwind..Customers
group by city
order by newid()

Libo said...

Excellent tip. I vote for the top operator with newid()