PL/SQL: Returning multiple rows into a comma separated string

I've spent my last days strugling to optimize a query, during one of my multiple desperate tries, I came across a crazy idea of dinamically build my query. This try have no results, but I read this example of data retrieval, and I didn't resist to write about it. So here's the code :

with data
   as
   (
      select myvalues, row_number() over (order by myvalues) rn, count(*) over () cnt
         from
         (
            select email_addr myvalues from customers where zip = 72204
         )
   )
select ltrim(sys_connect_by_path(myvalues, ','),',') catvalues
   from data
   where rn = cnt
   start with rn = 1
   connect by prior rn = rn-1;

This sample returns a comma separated string with all email addresses whith zip code 72204.

But the most important lesson from this sample was learning about hierarchically connect data in one single query.