The statistical aggregate functions (and their aliases) are:
stddev_pop (also stdevp) – standard deviation of a population. Computes the population standard deviation of the provided value expression evaluated for each row of the group (if distinct was specified, then each row that remains after duplicates have been eliminated), defined as the square root of the population variance.
stddev_samp (also stdev, stddev) – standard deviation of a sample. Computes the population standard deviation of the provided value expression evaluated for each row of the group (if distinct was specified, then each row that remains after duplicates have been eliminated), defined as the square root of the sample variance.
var_pop (also varp) – variance of a population. Computes the population variance of value expression evaluated for each row of the group (if distinct was specified, then each row that remains after duplicates have been eliminated), defined as the sum of squares of the difference of value expression from the mean of value expression, divided by the number of rows in the group.
var_samp (also var, variance) – variance of a sample. Computes the sample variance of value expression evaluated for each row of the group (if distinct was specified, then each row that remains after duplicates have been eliminated), defined as the sum of squares of the difference from the mean of the value expression, divided by one less than the number of rows in the group.
See Reference Manual: Building Blocks.
