When applied to "numeric" input, stddev_pop produces the same result as stddev_samp, and var_pop produces the same result as var_samp. This is because whoever wrote numeric_stddev_internal() forgot that the divisor is different for the sample case. This mistake is in fact visible in the regression test outputs for the function, so those outputs weren't checked very carefully :-(
regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match