oracle value exists in collection - collections

Question

I have function (used within a view) with the end result being a list of unique values from a row within a table of comma separated values.
Essentially given a table of:
studentid classes
12345 MATH 1301, HIST 1301, POLS 1301
57495 MATH 2309, HIST 1301
39485 MATH 1301, HIST 1301
I want to see
MATH 1301
MATH 2309
HIST 1301
POLS 1301
The below code works perfect if the source table is small, but when looking at a table of 30,000 rows I get the following error. ORA-06532: Subscript outside of limit
I'm pretty sure my problem is the collection is getting too large since it's getting duplicate values. The duplicate values in themselves only become a problem when the collection becomes too large. How do I keep the duplicate values out of the collection?
I've tried childnames.exists(element) but I believe this only works for seeing if there exists an element at the index value element correct? of I've looked at member of but I don't understand how to implement it.. Is there an easy way to check if a collection element exists? Or am I over looking something simple? Is there a different type other than odcivarchar2list that would allow a larger collection?
CREATE OR REPLACE FUNCTION unique_values_from_csv ( p_del VARCHAR2 := ',')
RETURN SYS.odcivarchar2list
IS
childnames SYS.odcivarchar2list := sys.odcivarchar2list ();
tempvar VARCHAR2(255);
l_idx PLS_INTEGER;
l_list2 VARCHAR2(32767) ;
l_value VARCHAR2(32767);
CURSOR tablewalker_cur
IS
SELECT distinct classes
FROM studentclasses;
BEGIN
FOR recordwalker_rec IN tablewalker_cur
LOOP
l_list2 := recordwalker_rec.classes;
LOOP
l_idx := INSTR (l_list2, p_del);
IF l_idx > 0
THEN
childnames.EXTEND;
tempvar := (LTRIM (RTRIM (SUBSTR (l_list2, 1, l_idx - 1))));
childnames (childnames.COUNT) := tempvar;
l_list2 := SUBSTR (l_list2, l_idx + LENGTH (p_del));
end if;
childnames.EXTEND;
childnames (childnames.COUNT) := (LTRIM (RTRIM (l_list2)));
EXIT;
END LOOP;
END LOOP;
RETURN childnames;
END unique_values_from_csv;
/

Answer 1

create or replace function unique_values_from_csv(p_del varchar2 := ',')
return sys.dbms_debug_vc2coll is
childnames sys.dbms_debug_vc2coll := sys.dbms_debug_vc2coll();
l_idx pls_integer;
l_list2 varchar2(32767) ;
procedure add_if_not_member(new_element varchar2) is
begin
if new_element not member of childnames then
childnames.extend;
childnames(childnames.count) := new_element;
end if;
end;
begin
for recordwalker_rec in (select distinct classes from studentclasses)
loop
l_list2 := recordwalker_rec.classes;
loop
l_idx := instr (l_list2, p_del);
if l_idx > 0 then
add_if_not_member(trim(substr (l_list2, 1, l_idx - 1)));
l_list2 := substr(l_list2, l_idx + length(p_del));
else
add_if_not_member(trim(l_list2));
exit;
end if;
end loop;
end loop;
return childnames;
end unique_values_from_csv;
/
Used SYS.DBMS_DEBUG_VC2COLL, which is a TABLE OF VARCHAR2(1000) and should support any number of elements. Although l_list2 varchar2(32767) will limit the results.
MEMBER OF is the correct condition.
Added an ELSE - the original function was only splitting the list in two.
Removed the cursor - for such a small query, another level of indirection isn't worth it.
Used TRIM() instead of LTRIM(RTRIM())
The best solution would be to throw out this function and stop storing non-atomic data in your database.
Here's some sample data and a query using the function:
create table studentclasses(studentid number, classes varchar2(4000));
insert into studentclasses
select 12345, 'MATH 1301,HIST 1301,POLS 1301' from dual union all
select 57495, 'MATH 2309,HIST 1301' from dual union all
select 39485, 'MATH 1301,HIST 1301' from dual;
commit;
select unique_values_from_csv from dual;
COLUMN_VALUE
MATH 1301
HIST 1301
POLS 1301
MATH 2309

Answer 2

select distinct
regexp_substr(classes, '([^,]+)(,\s*|$)', 1, occ, '', 1) as class
from
studentclasses,
(
select level as occ
from dual
connect by level <= (
select max(regexp_count(classes, ','))+1
from studentclasses
)
)
where
regexp_substr(classes, '([^,]+)(,\s*|$)', 1, occ, '', 1) is not null
order by 1