DELETE Collection Method in oracle work wrong - oracle

Question

I want to use DELETE Collection Method to delete some elements in collection
such as:
create or replace procedure testloop3 (clearaaa out nestedtable) as
type nestedtable is table of varchar2(255);
reply_ref_messageIds nestedtable;
getDelete_messageIds nestedtable;
begin
select distinct r.messagebox_id bulk collect into reply_ref_messageIds from reply r;
select m.id bulk collect into getDelete_messageIds from messagebox m;
getDelete_messageIds.delete(2);
getDelete_messageIds.delete(4);
getDelete_messageIds.delete(7);
getDelete_messageIds.delete(11);
getDelete_messageIds.delete(13);
for i in getDelete_messageIds.FIRST .. getDelete_messageIds.LAST loop
dbms_output.put_line(i);
end loop;
for i in 5 .. 12 loop
dbms_output.put_line(i);
end loop;
end;
and then I debug this procedure with plsql dev
-- Created on 2013/4/4 by THINKPAD
declare
-- Local variables here
aa nestedtable;
begin
-- Test statements here
testloop3(aa);
end;
and I get the indexes of getDelete_messageIds before remove which are 1 to 15.
However: when I debug to getDelete_messageIds.delete(2); it removes index 1 and 2...I can't explain why.
And then when I debug next statement getDelete_messageIds.delete(4); it removes index 3 and 4. And then getDelete_messageIds.delete(7); only removes index 7...
I can't understand...

Answer 1

your procedure, as posted, is showing nothing of the sort. you are simply looping around like
for idx in 1..15 loop
(.FIRST will resolve to 1 and .LAST will resolve to 15). it does not mean there are still 15 elements in the NT.
you are not checking to see if the indexes are deleted. I think you're confused about the proper way to loop through a nested table where there are gaps.
i.e. you can see the elements are deleted:
SQL> create table messagebox(id ) as select to_char(rownum) from dual connect by level <= 15;
Table created.
SQL> create or replace procedure testloop3
2 as
3 type nestedtable is table of varchar2(255);
4 getDelete_messageIds nestedtable;
5 v_idx number;
6 begin
7 select m.id bulk collect into getDelete_messageIds from messagebox m;
8 getDelete_messageIds.delete(2);
9 getDelete_messageIds.delete(4);
10 getDelete_messageIds.delete(7);
11 getDelete_messageIds.delete(11);
12 getDelete_messageIds.delete(13);
13 v_idx := getDelete_messageIds.first;
14 while v_idx is not null
15 loop
16 dbms_output.put_line(v_idx);
17 v_idx := getDelete_messageIds.next(v_idx);
18 end loop;
19 end;
20 /
Procedure created.
SQL> exec testloop3
1
3
5
6
8
9
10
12
14
15
so 2, 4, 7, 11, 13 are deleted. exactly as expected.

Answer 2

you can see
DECLARE
TYPE NumList IS TABLE OF NUMBER;
n NumList := NumList(1,3,5,7);
counter INTEGER;
BEGIN
DBMS_OUTPUT.PUT_LINE('N''s first subscript is ' || n.FIRST);
DBMS_OUTPUT.PUT_LINE('N''s last subscript is ' || n.LAST);
-- When the subscripts are consecutive starting at 1,
-- it's simple to loop through them.
FOR i IN n.FIRST .. n.LAST
LOOP
DBMS_OUTPUT.PUT_LINE('Element #' || i || ' = ' || n(i));
END LOOP;
n.DELETE(2); -- Delete second element.
-- When the subscripts have gaps
-- or the collection might be uninitialized,
-- the loop logic is more extensive.
-- Start at the first element
-- and look for the next element until there are no more.
IF n IS NOT NULL THEN
counter := n.FIRST;
WHILE counter IS NOT NULL
LOOP
DBMS_OUTPUT.PUT_LINE
('Element #' || counter || ' = ' || n(counter));
counter := n.NEXT(counter);
END LOOP;
ELSE
DBMS_OUTPUT.PUT_LINE('N is null, nothing to do.');
END IF;
END;
reference Finding the First or Last Collection Element