Elements order in Nested Tables

Question

In PL/SQL when I am adding element to a nested table of objects one by one(in order), and then trying to insert that nested table type to a physical table , the order of element changes. how can I prevent this behavior?

Answer 1

Your example is incomplete and has errors. Oracle does not guarantee the order of anything unless you use an order by clause. So, if you expect the following to produce rows in some order:
Open cur1 for select * from another_table;
then you need to add an order by clause, such as:
Open cur1 for select * from another_table order by id;
The following does minimal correction, completion, and provides sample data to demonstrate:
SCOTT@orcl_11gR2> create or replace TYPE coord AS OBJECT
  2    (id  number,
  3       x   number,
  4       y   number);
  5  /
Type created.
SCOTT@orcl_11gR2> create or replace TYPE coord_tab AS TABLE OF coord;
  2  /
Type created.
SCOTT@orcl_11gR2> create table demo_table
  2    (id     number,
  3       coords     coord_tab)
  4  NESTED TABLE coords STORE AS coords_tabb
  5  /
Table created.
SCOTT@orcl_11gR2> create table another_table
  2    (id  number,
  3       x   number,
  4       y   number)
  5  /
Table created.
SCOTT@orcl_11gR2> insert into another_table values (10, 20, 30)
  2  /
1 row created.
SCOTT@orcl_11gR2> insert into another_table values (60, 50, 40)
  2  /
1 row created.
SCOTT@orcl_11gR2> DECLARE
  2    type cur is ref cursor;
  3    cur1 cur;
  4    type rec_type is record
  5        (id  number,
  6         x   number,
  7         y   number);
  8    record_type rec_type;
  9    coords_tab coord_tab := coord_tab();
10    idx number := 1;
11  BEGIN
12    Open cur1 for select * from another_table order by id desc;
13    LOOP
14        fetch cur1 into record_type;
15        exit when cur1%notfound;
16        coords_tab.extend() ;
17        coords_tab(idx) := coord(record_type.id, record_type.x , record_type.y);
18        idx := idx + 1;
19    End LOOP;
20  --  EXECUTE IMMEDIATE 'insert into demo_table values (1,:1)' USING coords_tab ;
21    insert into demo_table values (1,coords_tab);
22  End;
23  /
PL/SQL procedure successfully completed.
SCOTT@orcl_11gR2> select * from demo_table
  2  /
        ID
COORDS(ID, X, Y)
         1
COORD_TAB(COORD(60, 50, 40), COORD(10, 20, 30))
1 row selected.
SCOTT@orcl_11gR2>