Select n random rows from SQL Server table

Question

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 wi

Answer 1

Didn't quite see this variation in the answers yet. I had an additional constraint where I needed, given an initial seed, to select the same set of rows each time.

For MS SQL:

Minimum example:

select top 10 percent *
from table_name
order by rand(checksum(*))

Normalized execution time: 1.00

NewId() example:

select top 10 percent *
from table_name
order by newid()

Normalized execution time: 1.02

NewId() is insignificantly slower than rand(checksum(*)), so you may not want to use it against large record sets.

Selection with Initial Seed:

declare @seed int
set @seed = Year(getdate()) * month(getdate()) /* any other initial seed here */

select top 10 percent *
from table_name
order by rand(checksum(*) % @seed) /* any other math function here */

If you need to select the same set given a seed, this seems to work.