Doubt on query

I have this table:

create table cat(

  cod integer, 

  cod_super integer,

  constraint cod_super_fk Foreign Key(cod_super) references cat(cod),

  constraint cod_pk Primary Key(cod)

);

insert into cat values(0, 1);

insert into cat values(1, 0);

insert into cat values(2, 0);

insert into cat values(3, 2);

insert into cat values(4, 3);

insert into cat values(5, 4);

The Query i want to do is:

• I want to know all the children´s and subchildrens.

Example 1: I want to know the children´s of 0 will return 1, 2, 3, 4, 5, 6, 7

Example 2: I want to know the children´s of 1 will return nothing