PG/PLSQL Function Exception

Question

I want to write a Postgres Function, which returns either a table or an error after i pass a value to it. For Example: Looking for the owner of a smartphone works.

create or replace function get_handy_besitzer (ide int) 
    returns table (
        h_kostenstellename varchar,
        h_edvkennung varchar,
        h_bezeichnung varchar
    ) 
    language plpgsql
as $$
begin


    return query 
        select
            kostenstellename,
            edvkennung,
            bezeichnung
        from
            anlagen
        where
            id = ide;
            
        
        
            
end;$$

But when i put the excpetion at the end like

create or replace function get_handy_besitzer (ide int) 
    returns table (
        h_kostenstellename varchar,
        h_edvkennung varchar,
        h_bezeichnung varchar
    ) 
    language plpgsql
as $$
begin


    return query 
        select
            kostenstellename,
            edvkennung,
            bezeichnung
        from
            anlagen
        where
            id = ide;
            
        exception 
        when no_data_found then 
          raise exception 'id not found';
        
            
end;$$

it doesn't work. But why?

I tried using the record type as a return, but that resulted in another error. I really dont know what to do, i dont even find any example with a function that handles exceptions.

Edit: My goal is to specify the exception for certain sql states like

       exception 
       when sqlstate 'P0002' then 
          raise exception 'id not found';

       exception 
       when sqlstate '22P02' then 
          raise exception 'try it with a number';

Answer 1

Your function is intended to raise an exception, not to handle one.

    return query 
        select
            kostenstellename,
            edvkennung,
            bezeichnung
        from
            anlagen
        where
            id = ide;

    if not found then
        raise exception 'no data found';
    end if;

Read about Reporting Errors and Messages and Obtaining the Result Status