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#### 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):

 ::= [ `ARITHMETIC`] `MEAN` | `HARMONIC MEAN` | `GEOMETRIC MEAN` | `MEDIAN` | `STANDARD DEVIATION` | `VARIANCE` | ```MEDIAN ABSOLUTE DEVIATION``` | `SUM` | `MINIMUM` | `MAXIMUM` | `FINAL` | `PERCENTILE`

`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.

Scott Pakin, pakin@lanl.gov