NewID() is a really useful SQL function, since it's resolved on a per row rather than per query basis. That comes in handy if you want random values for each row in a table.
For example, this (ad-hoc) query will update your [datefield] with a random date within the past five days:
update [tablename]There's another (more well known) trick for getting results back in random order that I might as well mention while I'm at it:
set [datefield] =
cast(getdate() as int)
-5*rand(cast(cast(newid() as binary(8)) as int))
select * from [tablename] order by newid()