evil.sql

create function polycast(input text, typ anyelement) returns anyelement language plpgsql immutable as
$$
begin
  return input::anyelement;
end;
$$;

create function nullable(input text, typ anyelement) returns anyelement language plpgsql immutable as
$$
begin
        return polycast(input, typ);
exception
when others then
        return typ;
end;$$;

postgres=# select 1 where nullable('abc',  null::timestamptz) < nullable('2018-01-01 00:00:00',  null::timestamptz);
 ?column? 
----------
(0 rows)

postgres=# select 1 where nullable('2018-01-01 00:00:00',  null::timestamptz) < nullable('2018-01-01 10:00:00',  null::timestamptz);
 ?column? 
----------
        1
(1 row)

postgres=# select 1 where nullable('2018',  null::numeric) < nullable('2019',  null::numeric);
 ?column? 
----------
        1