Oracle does things a bit differently than you might expect - so you will run into trouble if you just copy methods from other databases:
- You create the GTT only once, before you write any PL/SQL (You don't have CREATE or DROP in the routine).
- Each session sees a view of the GTT which is independent of any other session. You just use it as if it had been created specially for you alone.
As Gandolf say, this may not be the best way.
"The power of instruction is seldom of much efficacy except in those happy dispositions where it is almost superfluous" - Gibbon, quoted by R.P.Feynman