Nested Cursor & Recursion in PL/SQL - recursion

Question

I'm new to PL/SQL and have just started working with cursors. I'm writing a small program to print the recursive trace for an employee -> supervisor all the way to the big boss. Essentially my query will output employee, supervisor1, then output supervisor1, supervisor2, all the way to supervisorn, null. My goal is to write a short PL/SQL program that will iterate this process for each employee. My code is as follows:
set serveroutput on;
DECLARE
v_iteration number := 0;
BEGIN
for x in (select * from e)
loop
dbms_output.put_line('recursive trace #' || v_iteration);
v_iteration := v_iteration + 1;
for y in
(WITH sup_hierarch (employee, supervisor) AS
(select x.ssn, x.superssn FROM e
UNION ALL
select supervisor, superssn
from sup_hierarch join e on sup_hierarch.supervisor = e.ssn
where sup_hierarch.supervisor is not null)
select * from sup_hierarch)
loop
dbms_output.put_line(y.employee || ', ' || y.supervisor);
end loop;
end loop;
END;
/
I've used two implicit cursors, the outer implicit cursor is used to loop through the employee table (in order to print the recursive trace for each employee), and the inner implicit cursor is used to loop through the recursive trace itself. The code somewhat works, sample output:
recursive trace #6
666884444, 333445555
666884444, 333445555
666884444, 333445555
666884444, 333445555
666884444, 333445555
666884444, 333445555
666884444, 333445555
666884444, 333445555
333445555, 888665555
333445555, 888665555
333445555, 888665555
333445555, 888665555
333445555, 888665555
333445555, 888665555
333445555, 888665555
333445555, 888665555
888665555,
888665555,
888665555,
888665555,
888665555,
888665555,
888665555,
888665555,
Based on the entirety of my output, the loop through each employee is working correctly. Furthermore, the recursive trace for each employee is working correctly (that is, each employee has correct recursive depth & stack). However, each line in the recursive trace is printing number_of_employee times, when I expected it to be printed once. Why is this?

Answer 1

The problem with your code is the first part of your WITH clause: it returns the same date for as many rows as there are in 'e'.
Why not just do it like this:
DECLARE
v_iteration number := 0; -- useless in the version
BEGIN
for y in
(WITH sup_hierarch (employee, supervisor) AS
(select x.ssn, x.superssn FROM e
UNION ALL
select supervisor, superssn
from sup_hierarch join e on sup_hierarch.supervisor = e.ssn
where sup_hierarch.supervisor is not null)
select * from sup_hierarch)
loop
dbms_output.put_line(y.employee || ', ' || y.supervisor);
end loop;
END;
/
and if you want 2 loops, just to get your iterations:
DECLARE
v_iteration number := 0;
BEGIN
for x in (select * from e)
loop
dbms_output.put_line('recursive trace #' || v_iteration);
v_iteration := v_iteration + 1;
for y in
(WITH sup_hierarch (employee, supervisor) AS
(select x.ssn, x.superssn FROM dual
UNION ALL
select supervisor, superssn
from sup_hierarch join e on sup_hierarch.supervisor = e.ssn
where sup_hierarch.supervisor is not null)
select * from sup_hierarch)
loop
dbms_output.put_line(y.employee || ', ' || y.supervisor);
end loop;
end loop;
END;
/