As I’ve often pointed out, this blog isn’t AskTom, or the OTN forum, so I don’t expect to have people asking me to solve their problems; neither do I answer email questions about specific problems. Occasionally, though, questions do appear that are worth a little public airing, and one of these came in by email a couple of weeks ago. The question is longer than the answer I sent, my contribution to the exchange doesn’t start until the heading: “My Reply”.
Last week I find a very interesting thing about use_hash hint accidentally. That is when you have join two tables using unique column from one table and you have a equal predicate on that column, you cannot use hint to make them using hash join. I know that it does not make sense to use hash join in this case because nested loop is the best way to do it. The point is why Oracle ignore the hint here.
