PERCENTILE_CONT

[rchui]

Is your feature request related to a problem? Please describe.

PERCENTILE_CONT is used to compute a given percentile value on a continuous distribution of an input column. This is useful for a variety of statistical calculations. It is also a standard Postgres function.

Describe the solution you'd like

I would like PERCENTILE_CONT to be implemented (https://www.postgresql.org/docs/9.4/functions-aggregate.html) so that it is usable in RisingWave.

Describe alternatives you've considered

Computing this value in SQL would be quite difficult.

You could potentially use the UDF server to work around this limitation.

Additional context

No response

[fuyufjh]

duplicated #12857