I have created a UDF using:

%sql

CREATE OR REPLACE FUNCTION f_timestamp_max()....

And I've confirmed it works with:

%sql

select f_timestamp_max()

But when I try to use it in a Window function (lead over partition), I get:

AnalysisException: Using SQL function 'default.f_timestamp_max' in Window is not supported.

Can anyone share a way of being able to do this?