Aggregate percentile(TYPE d, float rank) TYPE

d - Operates on floats or decimals.
rank - The threshold percentage.
Return the value in the window which has the specified percentage of the window smaller than it.

Returns a value R from the window where rank percent of the other values in the window is smaller than R.

Values of NaN are ignored. Positive infinities are larger than any other number and negative infinities are smaller than any other number. Positive or negative infinity will be returned if the specified rank falls within infinite values.

If the window is empty, then NaN is returned.