select sum((qty-mean)*square(qty-mean)
       /(N*sigma*square(sigma))) as skew,
       sum(square(square(qty-mean))
       /(N*square(square(sigma))))-3 as ExcessKurtosis
from pubs..sales,
(
  select
    avg(qty) as mean,
    stdev(qty) as sigma,
    count(qty) as N
  from pubs..sales
) S