How to retrieve distinct values from nested table in Oracle - oracle

Question

I have a problem where in I need to retrieve distinct values out of a nested table collection.
Example code:
FUNCTION get_part_atts
( p_gp_id IN dummy_di_parts.di_gp_id%TYPE
, p_attribute_name IN dummy_part_attr_def.attribute_name%TYPE
, p_sel1 IN dummy_di_part_atts.sel1%TYPE DEFAULT NULL
, p_sel2 IN dummy_di_part_atts.sel2%TYPE DEFAULT NULL
, p_sel3 IN dummy_di_part_atts.sel3%TYPE DEFAULT NULL )
RETURN dummy_pkg.part_atts_tabtype
RESULT_CACHE
IS
l_dummy_part_seq dummy_di_parts.dummy_part_seq%TYPE;
l_attribute_id dummy_part_attr_def.attribute_id%TYPE;
l_default_value dummy_part_attr_def.default_value%TYPE;
l_return part_atts_tabtype := part_atts_tabtype();
BEGIN
SELECT p.dummy_part_seq
INTO l_dummy_part_seq
FROM dummy_di_parts p
WHERE p.di_gp_id = p_gp_id
AND p.di_part_status = 'ACTIVE';
EXCEPTION
WHEN NO_DATA_FOUND
THEN RAISE_APPLICATION_ERROR(-20021,'No active parts found '||p_gp_id||'.');
WHEN TOO_MANY_ROWS
THEN RAISE_APPLICATION_ERROR(-20022,'More than one active part '||p_gp_id||'.');
END part_lookup;
BEGIN
SELECT pad.attribute_id
, pad.default_value
INTO l_attribute_id
, l_default_value
FROM dummy_part_attr_def pad
WHERE pad.attribute_name = p_attribute_name;
EXCEPTION
WHEN NO_DATA_FOUND
THEN RAISE_APPLICATION_ERROR(-20023,p_attribute_name||' is not a valid attribute name.');
END attribute_def_lookup;
SELECT pa.attribute_value
BULK COLLECT INTO l_return
FROM dummy_di_part_atts pa
WHERE pa.dummy_part_seq = l_dummy_part_seq
AND pa.attribute_id = l_attribute_id
AND ( p_sel1 IS NULL OR
pa.sel1 = p_sel1 )
AND ( p_sel2 IS NULL OR
pa.sel2 = p_sel2 )
AND ( p_sel3 IS NULL OR
pa.sel3 = p_sel3 );
RETURN l_return;
END get_part_atts;
Now I need to select Distinct from the collection l_return which is a nested table type
Please help

Answer 1

In Oracle 12C you can do this:
select distinct attribute_value
from table (get_part_atts(...))
Prior to 12C you could do similar, but only if the type was defined in the database using CREATE TYPE rather than declared in a package specification.

Answer 2

Try using "multiset union distinct". For example, a function that splits a delimited string into tokens and returns a nested table:
CREATE OR REPLACE function fn_split(i_string in varchar2, i_delimiter in varchar2 default ',', b_dedup_tokens in number default 0)
return sys.dbms_debug_vc2coll
as
l_tab sys.dbms_debug_vc2coll;
begin
select regexp_substr(i_string,'[^' || i_delimiter || ']+', 1, level)
bulk collect into l_tab
from dual
connect by regexp_substr(i_string, '[^' || i_delimiter || ']+', 1, level) is not null
order by level;
if (b_dedup_tokens > 0) then
return l_tab multiset union distinct l_tab;
end if;
return l_tab;
end;
Testing:
select * from table(fn_split('x,x,y,z', ',', 1));
Output:
COLUMN_VALUE
x
y
z