What is the purpose of "RETURN AS VALUE" in NESTED TABLES (Oracle 9i) - oracle

Question

Is there a specific case, when i should use RETURN AS VALUE?
Normally i use only NESTED TABLE xxx STORE AS xxx
For example:
CREATE OR REPLACE TYPE address_t AS OBJECT (
ADDID NUMBER(10,0),
STREET VARCHAR2(40),
ZIP VARCHAR2(5),
CITY VARCHAR2(40)
)
/
CREATE OR REPLACE TYPE addresses_nt AS TABLE OF address_t
/
CREATE OR REPLACE TYPE invoicepos_t AS OBJECT (
ARTID NUMBER(10,0),
AMOUNT NUMBER(10,0)
)
/
CREATE OR REPLACE TYPE invoicepos_nt AS TABLE OF invoicepos_t
/
CREATE OR REPLACE TYPE customer_t AS OBJECT (
CUSID NUMBER(10,0),
FIRSTNAME VARCHAR2(30),
LASTNAME VARCHAR2(30),
ADDRESSES addresses_nt
)
/
CREATE OR REPLACE TYPE invoice_t AS OBJECT (
INVOICEID NUMBER(10,0),
CUSTOMER REF customer_t,
ADDID NUMBER(10,0),
POSITIONS invoicepos_nt
)
/
CREATE TABLE customer OF customer_t
NESTED TABLE ADDRESSES STORE AS all_adresses RETURN AS VALUE
/
CREATE TABLE invoices OF invoice_t
NESTED TABLE POSITIONS STORE AS all_invoicepos RETURN AS VALUE
/

Answer 1

As far as I can tell, the only difference is that LOCATORs are a bit faster than VALUEs. But that doesn't make sense and I'm hoping somebody will prove me wrong; there's almost never a "fast=true" switch.
According to the SQL Language Reference:
RETURN [AS] Specify what Oracle Database returns as the result of a query.
VALUE returns a copy of the nested table itself.
LOCATOR returns a collection locator to the copy of the nested table.
The locator is scoped to the session and cannot be used across sessions. Unlike a LOB locator, the collection locator cannot be used to modify the collection instance.
This implies that LOCATORs are read-only. But on 11gR2 a LOCATOR can still be modified.
The Object Relational Developer's Guide also discusses LOCATORs, but does not mention any downsides to using them.
Sample Schema
CREATE OR REPLACE TYPE invoicepos_t AS OBJECT (
ARTID NUMBER(10,0),
AMOUNT NUMBER(10,0)
)
/
CREATE OR REPLACE TYPE invoicepos_nt AS TABLE OF invoicepos_t
/
create table invoices_val
(
INVOICEID NUMBER,
POSITIONS invoicepos_nt
)
NESTED TABLE POSITIONS STORE AS all_invoicepos_val RETURN AS VALUE
/
create table invoices_loc
(
INVOICEID NUMBER,
POSITIONS invoicepos_nt
)
NESTED TABLE POSITIONS STORE AS all_invoicepos_loc RETURN AS locator
/
insert into invoices_val values(1, invoicepos_nt(invoicepos_t(1,1)));
insert into invoices_loc values(1, invoicepos_nt(invoicepos_t(1,1)));
insert into invoices_def values(1, invoicepos_nt(invoicepos_t(1,1)));
commit;
Compare performance and funcionality
--Value: 1.0 seconds
declare
v_positions invoicepos_nt;
begin
for i in 1 .. 10000 loop
select positions
into v_positions
from invoices_val;
end loop;
v_positions.extend;
v_positions(2) := invoicepos_t(3,3);
update invoices_val set positions = v_positions;
end;
/
--Locator: 0.8 seconds
declare
v_positions invoicepos_nt;
begin
for i in 1 .. 10000 loop
select positions
into v_positions
from invoices_loc;
end loop;
v_positions.extend;
v_positions(2) := invoicepos_t(3,3);
update invoices_loc set positions = v_positions;
end;
/