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The SQL implementation provides the well-known standard statistical aggregates COUNT, SUM, AVG, MIN and MAX over scalar types and groupings. In addition, a few important statistical aggregate functions: MEDIAN, QUANTILE, and correlation CORR are available. The percentile is a float value between 0.0 and 1.0. MEDIAN(<expr>) is equivalent to QUANTILE(<expr>,0.5). 

STDDEV_SAMP computes the cumulative sample standard deviation and returns the square root of the sample variance. STDDEV_POP computes the population standard deviation and returns the square root of the population variance. Both functions take takes as an argument any numeric datatype.
Likewise, VAR_SAMP and VAR_POP function returns the sample variance (/n-1) of a set of numbers and the biased variance (/n) of a set of numbers, respectively.

      QUANTILE  '(' scalar_expr ',' scalar_expr ')'
    | STDDEV_SAMP '(' scalar_expr')
    | STDDEV_POP '(' scalar_expr')
    | VAR_SAMP '(' scalar_expr')
    | VAR_POP '(' scalar_expr')
    | MEDIAN '(' scalar_expr')'
    | CORR '(' scalar_expr',' scalar_expr ')'