How to display all parent regions (repeatedly reference cursor)?

Question

CREATE TABLE regions
PARENT_NAME VARCHAR2(30),
CHILD_NAME VARCHAR2(30)
INSERT INTO regions VALUES(NULL,'Asia');
INSERT INTO regions VALUES(NULL,'Australia');
INSERT INTO regions VALUES(NULL,'Europe');
INSERT INTO regions VALUES(NULL,'North America');
INSERT INTO regions VALUES('Asia','China');
INSERT INTO regions VALUES('Asia','Japan');
INSERT INTO regions VALUES('Australia','New South Wales');
INSERT INTO regions VALUES('New South Wales','Sydney');
INSERT INTO regions VALUES('Canada','Ontario');
INSERT INTO regions VALUES('China','Beijing');
INSERT INTO regions VALUES('England','London');
INSERT INTO regions VALUES('Europe','United Kingdom');
INSERT INTO regions VALUES('Illinois','Aurora');
INSERT INTO regions VALUES('Illinois','Chicago');
INSERT INTO regions VALUES('Illinois','Rockford');
INSERT INTO regions VALUES('Japan','Osaka');
INSERT INTO regions VALUES('Japan','Tokyo');
INSERT INTO regions VALUES('North America','Canada');
INSERT INTO regions VALUES('North America','United States');
INSERT INTO regions VALUES('Ontario','Ottawa');
INSERT INTO regions VALUES('Ontario','Toronto');
INSERT INTO regions VALUES('United States','Colorado');
INSERT INTO regions VALUES('United States','Illinois');
INSERT INTO regions VALUES('United States','Texas');
INSERT INTO regions VALUES('United Kingdom','England');
COMMIT;
Based on the REGIONS table, write a PL/SQL anonymous block that accepts a region name from the user input and display all its parent regions.
right now this is what I have so far:
ACCEPT p_1 PROMPT 'Please enter the region name: '
DECLARE
v_rname regions.child_name%type := '&p_1';
v_count number;
v_counter number := 0;
v_parent regions.parent_name%type;
v_child regions.child_name%type;
cursor reg_cur is
select parent_name, child_name from regions;
BEGIN
open reg_cur;
fetch reg_cur into v_parent, v_child;
select count(*) into v_count
from regions
where upper(child_name) = upper(v_rname);
if v_count = 0 then
dbms_output.put_line(v_rname || ' is not in the regions table.');
else
while reg_cur%found loop
if upper(v_rname) = upper(v_child) then
if v_parent is null then
v_parent := v_child;
dbms_output.put_line(v_count || ') ' || upper(v_parent));
else
dbms_output.put_line(v_count || ') ' || rpad(upper(v_rname), 20) || '<<<<<' || lpad(upper(v_parent), 10));
end if;
end if;
fetch reg_cur into v_parent, v_child;
end loop;
end if;
close reg_cur;
END;
if user inputs 'chicago' my query returns only a single parent. I'm not certain how to keep referencing the cursor so that I could output the rest of the parent_names and child_names until parent becomes null
the output should be:
chicago <<<<< illinois
illinois <<<<< united states
united states <<<<< North america

Answer 1

Hi,
If you have to do this in PL/SQL, then why don't you use Solomon's solution in PL/SQL?
BEGIN
     FOR  regions_info  IN
               select  child_name || ' <<<<< ' || parent_name     AS txt
                   from       regions
                   where      parent_name      is not null
                   start with      child_name      = '&p_1'
                   connect by      child_name      = prior parent_name
     LOOP
          dbms_output.put_line (regions_info.txt);
     END LOOP;
END;
/However, if you want to see what's happening with your code, add some code to make sure you don't get into an infinite loop. I used the local variable v_counter (which you had declared, but not used for anything else) to count how many times you had gone through the loop, and EXIT once you reach 100 times.
Also, add some more calls to dbms_output, so you can see what's going on.
For example:
     else
          v_counter := 0;
          loop
               v_counter := v_counter + 1;
               EXIT WHEN  v_counter > 100;
               dbms_output.put_line (  v_child   || ' = v_child, '
                              || v_parent  || ' = v_parent in LOOP'
               open reg_cur;
               fetch reg_cur into v_child, v_parent;
               if upper(v_rname) = upper(v_child) then
                    dbms_output.put_line(v_counter + 1 || ') ' || rpad(upper(v_child), 20) || '<<<<<' || lpad(upper(v_parent), 10));
               end if;
               fetch reg_cur into v_child, v_parent;
               close reg_cur;
               v_parent := v_child;
               exit when v_parent is null;
          end loop;
...Make sure you issue the SQL*Plus command
SET   SERVEROUTPUT   ONbefore running this; otherwise, you won't see the output from put_line.
What do you see?
Do you understand why you're in an infinite loop?
Do you really want the cursor to do exactly the same thing every time you call it?
Maybe you should add a parameter to the cursor, which can be used in, say, a WHERE clause.
Edited by: Frank Kulash on Feb 2, 2011 11:50 PM