> So I'd take it that PostgreSQL's STDDEV implements STDDEV_POP.
A simple test (3 rows, values 1, 2, and 3) shows that pgsql uses the
sample (N-1) formulas for variance and standard deviation, not the
population (N) formulas.
Oracle, which also implements the sample formulas, specifically defines
the variance to be 0 when there is just one row.
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Mike Nolan