SQL Question

[stecal]

Three issues.
1) You could provide more information about the size and scope of things you want to have done when you first post your question. Are you asking about a million records because you don't believe it can be done, or because you think I am stupid for suggesting the PL/SQL approach? That's just one way to do things.
2) Setting the methodology aside for the moment, based on your problem statement (checking records in a temp table against a master table, then inserting or updating depending on the case), does it not strike you as being obvious that you will be doing a record-by-record comparison in some form or another? The insert case is simple. Not there, insert it. What is your update criteria? How else will you know what to do with a record in the temp table?
3) Is PL/SQL the best way for your application? Who knows? Maybe you should consider COBOL or some other procedural call to do the work. You can look in just about any programming logic book and see how this problem is done - on a daily basis by a gazillion companies dealing with a bazillion records. Banking/updating customer accounts is a typical example of comparing a record in a temp table to a master table.