select case when char_length('1.2.3.4.5')< char_length(replace('1.2.3.4.5','.',''))+4 then 1 else 0 end, char_length('1.2.3.4.5'), char_length(replace('1.2.3.4.5','.',''))+4;

CREATE OR REPLACE FUNCTION aws_sqlserver_ext.parsename(
    object_name varchar,
    object_piece integer) 
    RETURNS VARCHAR AS $$
select case when char_length('$1')< char_length(replace('$1','.',''))+4 and $2 between 1 and 4 then reverse(split_part(reverse($1),'.',$2)) else '' END

$$ immutable LANGUAGE 'sql';

select aws_sqlserver_ext.parsename(n,k), k
from
(values 
('1.2.3.4.5')
) as t(n) 
cross join 
(select k from (values (1),(2),(3),(4),(5),(0),(-1)) t1(k)) t1
order by n,k

select case when char_length($1)< char_length(replace($1,'.',''))+4 and $2 between 1 and 4 then reverse(split_part(reverse($1),'.',$2))