John M Gant John M Gant - 9 months ago 27
SQL Question

Select n random rows from SQL Server table

I've got a SQL Server table with about 50,000 rows in it. I want to select about 5,000 of those rows at random. I've thought of a complicated way, creating a temp table with a "random number" column, copying my table into that, looping through the temp table and updating each row with

, and then selecting from that table where the random number column < 0.1. I'm looking for a simpler way to do it, in a single statement if possible.

This article suggest using the
function. That looks promising, but I can't see how I could reliably select a certain percentage of rows.

Anybody ever do this before? Any ideas?

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.