SQL random sample with groups

Question

I have a university graduate database and would like to extract a random sample of data of around 1000 records.

I want to ensure the sample is representative of the pop

Answer 1

It is not necessary to partition the population at all.

If you are taking a sample of 1000 from a population among hundreds of course codes, it stands to reason that many of those course codes will not be selected at all in any one sampling.

If the population is uniform (say, a continuous sequence of student IDs), a uniformly-distributed sample will automatically be representative of population weighting by course code. Since newid() is a uniform random sampler, you're good to go out of the box.

The only wrinkle that you might encounter is if a student ID is a associated with multiple course codes. In this case make a unique list (temporary table or subquery) containing a sequential id, student id and course code, sample the sequential id from it, grouping by student id to remove duplicates.