Building Random Number Ranges

Kevin Feasel

2017-06-26

T-SQL

David Fowler shows how to generate a random number for each record in a result set:

Hmmmmm…. It looks like we’ve got the same number for every person, that wasn’t what we wanted.  And that’s my issue with RAND(), it’ll give you a different random number every time it runs but if run as part of a query it’ll always return the same number for every row returned.

So what else can we do?  We’ll there is something that gives us a ‘random’ value for every row in the query and that’s our good old friend NEWID().  Let’s try the same query but this time we’ll swap RAND() with NEWID().

One major use case for this is sampling data sets for model training and testing:  if you pull from a range of 1-10, you could perhaps train against 1-5, cross-validate against 6-7, and test against 8-10.  Doing this instead of TOP X% reduces the likelihood of sampling bias.

Related Posts

Reading SQL Server Error Logs

Thomas Rushton has a script for us: Why Script This? What’s Wrong With SSMS’s GUI?Well, although SSMS does allow you to look at the error logs, it’s not very helpful for filtering – you can only filter for items that match, rather than exclude items. There are a few other filters as well – I […]

Read More

Rounding to Intervals in Various Languages

Dave Mason doesn’t like rounding to intervals very much in T-SQL: If I had to choose any of these options for production, I’d probably go with Query 1, just because I think it would make the most sense to any other developer that might encounter it (including future me, who probably wouldn’t remember writing the […]

Read More

Categories

June 2017
MTWTFSS
« May Jul »
 1234
567891011
12131415161718
19202122232425
2627282930