4.2.4 Aggregate functions

The following functions, referred to collectively as <aggr_func>s, may be used in an aggregate expression (see Aggregate expressions):

MEAN and ARITHMETIC MEAN are equivalent. MEDIAN is the value such that there are as many larger as smaller values. If there are an even number of values, MEDIAN is the arithmetic mean of the two medians. FINAL returns only the final value measured. PERCENTILE returns a given percentile, <expr>, of the values. <expr> must lie in the range [0, 100]. Percentile values are computed as x_g + (h - g)(x_g - x_h), where x is the data in sorted order and h is (|x| - 1) * p/100 + 1 when computing the value at the pth percentile. (See Wikipedia’s entry on quantile for more information.) The interpretation of the remaining aggregate functions should be unambiguous.