Global temp table and edit

Question

Hi all,
Can someone tell me why when I create a GTT and insert the data like the followijng ,I get insert 14 rows msg. But when I do a select statement from sqlwork shop , sometimes i get the data sometimes I don't. my understanding is this data is supposed to stay during my logon session then got cleaned out when I exit session.
I am developing a screen in apex and will use this temp table for user to do some editing work. Once ithe editing is done then I save the data into a static table. Can this be done ? So far my every attempt to update the temp table always result to 0 rows updated and the temp table reversed back to 0 rows. CAn you help me ?
CREATE GLOBAL TEMPORARY TABLE "EMP_SESSION"
(     "EMPNO" NUMBER NOT NULL ENABLE,
     "ENAME" VARCHAR2(10),
     "JOB" VARCHAR2(9),
     "MGR" NUMBER,
     "HIREDATE" DATE,
     "SAL" NUMBER,
     "COMM" NUMBER,
     "DEPTNO" NUMBER
) ON COMMIT PRESERVE ROWS
insert into emp_session( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
select * from emp
select * from emp_session
-- sometimes I get 14 rows, sometimes 0 rows
Thanks.
Tai

Answer 1

Tai,
To say that Apex doesn't support GTT's is not quite correct. In order to understand why it is not working for you and how they may be of use in an Apex application, you have to understand the concept of a session in Apex as opposed to a conventional database session.
In a conventional database session, as when you are connected with sqlplus then you have what is known as a dedicated session, or a synchronous connection. Temporary objects such as GTTs and packaged variables can persist across calls to the database. A session in Apex however is asynchronous by nature and a connection to the database is done through some sort of a server such as the Oracle HTTP server or the Apex Listener, which in effect maintains a pool of connections to the database and calls by your application aren't guaranteed to get the same connection for each call.
To get over this, the guys who developed Apex came up with various methods to maintain session state and global objects that are persistent within the context of an Apex session. One of these is Apex collections, which are a device for maintaining collection like (array like) data that is persistent within an Apex session. These are Apex session specific objects in that they are local to the session that creates and maintains them.
With this knowledge, you can then see why the GTT is not working for you and also how a GTT may be of use in an Apex application, provided you don't expect the data to persist across a call, as in a PL/SQL procedure. You should note though, that unless you are dealing with very large datasets, then a regular Oracle collection is preferable.
I hope this explains your issue.
Regards
Andre