select * from tbl TABLESAMPLE system (5)
The SYSTEM method is significantly faster than the BERNOULLI method when small sampling percentages are specified, but it may return a less-random sample of the table as a result of clustering effects.
WHERE some_col > ''
Since null > '' produces unknown, this has the effect of filtering out both null and empty strings.
@JoshPinter: coalesce(some_col, '') = ''