>>>>Actually, then I heard from someone, in a discussion on the subject, that the most complicated and largest contraption in use, an ocean liner, didn't go deeper than ten levels.
>>>
>>>Last statement is interesting. Of course, once you go beyond one level the only approach that makes sense is a self-referencing/recursive one.
>>>
>>
>>Which fits the general rule that in the database business, there are only three quantities: 0, 1 and many.
>>
>
>Don't forget null. We just don't know about those.

So the answer to "how many" is, generally, "none", "one", "many" and "dunno", where "many" is limited by available memory.

I've heard that the official list of genders in one country (forgot which) is 7 rows long.

>I can't tell you how many problems I have run into involving nulls. Now at least I am proactive about it but it's an ongoing battle.

I wouldn't know about that.

(just kidding... during the last week I wrote nvl() about 400 times)