How do I CREATE IF NOT EXISTS Temp table in PLSQL?

Question

hello, how do I CREATE IF NOT EXISTS Temp table in PLSQL? The following table is to be created in FIRST call inside a recursive function (which you'll see in QUESTION 2).
QUESTION 1:
CREATE GLOBAL TEMPORARY TABLE TmpHierarchyMap
                              Id numeric(19,0) NOT NULL,
                              ParentId numeric(19,0) NOT NULL,
                              ChildId numeric(19,0) NOT NULL,
... more ...
                         ) on commit delete rows');
QUESTION 2: How to return a temp table from a function?
For example, this is how I'm doing it at the moment, using Nested Table.
EXECUTE IMMEDIATE 'CREATE OR REPLACE TYPE TmpHierarchyMapObjType AS OBJECT
               Id numeric(19,0) ,
               ParentId numeric(19,0),
               ChildId numeric(19,0),
... more ...
     EXECUTE IMMEDIATE 'CREATE OR REPLACE TYPE TmpHierarchyMapTableType AS TABLE OF TmpHierarchyMapObjType;';
CREATE OR REPLACE FUNCTION fnGetParentsTable
ObjectId number,
ObjectClassifier varchar2
RETURN TmpHierarchyMapTableType
IS
TmpHierarchyMap TmpHierarchyMapTableType := TmpHierarchyMapTableType();
ThisTempId varchar2(32);
CURSOR spGetParents_cursor IS
SELECT
Id,
ParentId,
ChildId,
FROM TMP_HIERARCHYMAP
WHERE TempId = ThisTempId;
BEGIN
SELECT sys_guid() INTO ThisTempId FROM dual;
spRecursiveGetParents(ObjectId, ObjectClassifier, ThisTempId);
FOR oMap in spGetParents_cursor LOOP
TmpHierarchyMap.Extend();
TmpHierarchyMap(TmpHierarchyMap.Count) := TmpHierarchyMapObjType( oMap.Id
, oMap.ParentId
, oMap.ChildId
END LOOP;
DELETE FROM TMP_HIERARCHYMAP WHERE TempId = ThisTempId;
RETURN TmpHierarchyMap;
END fnGetParentsTable;
QUESTION 3: what does the word GLOBAL means? I read that temp table is visible only to a particular database connection/session and will be dropped automatically on termination of the session. i can only find this information in some forum discussion but failed to locate this in Oracle doc, can someone point me in right direction please?
Many thanks!
REF:
http://stackoverflow.com/questions/221822/sybase-developer-asks-how-to-create-a-temporary-table-in-oracle
http://www.oracle-base.com/articles/8i/TemporaryTables.php

Answer 1

devvvy wrote:
so if I CREATE GLOBAL TEMPORARY TABLE twice on second pass of my recursive function what then...?You don't create it inside your function.
You create the GTT once on your database outside of the function and then just leave it there and use it.
Tables should not be dynamically created and dropped.
Only other database engines such as SQL Server use the concept of creating temporary tables during the execution of code. Oracle uses a "create once, use whenever" methodology.