Issue found on page 'Aggregate Functions': quantile_cont(x, pos) aggregate function takes value in the range [-1, 1] for pos, needs documentation

[rpbouman]

The docs for aggregate function quantile_cont(x, pos) read:

The interpolated pos-quantile of x for 0 <= pos <= 1,

But when we enter an out of range value, the error message tells us the range for pos is [-1, 1]:

select quantile_cont(x, 2)
from range(0,100) as T(x)

output:

Binder Error: QUANTILE can only take parameters in the range [-1, 1]

When I try to use negative values within the range, it appears as if negative values are interpreted to "counting backwards", as if for for 0 < y <=1,

quantile_cont(x, -y)
is equivalent to
quantile_cont(x, 1-y)

For example:

SELECT quantile_cont(x, -0.1)    as "q-0.1"
,      quantile_cont(x, 1 - 0.1) as "q1-0.1"
,      "q-0.1" = "q1-0.1" as "eq"
from range(0, 100) as T(x)

output:

┌───────────────────┬───────────────────┬─────────┐
│       q-0.1       │      q1-0.1       │   eq    │
│      double       │      double       │ boolean │
├───────────────────┼───────────────────┼─────────┤
│ 89.10000000000001 │ 89.10000000000001 │ true    │
└───────────────────┴───────────────────┴─────────┘

Page URL: https://duckdb.org/docs/sql/functions/aggregates.html

[szarnyasg]

Cross-linking #3305