On Sun, 2008-02-10 at 03:08 -0500, Lew wrote: > SunWuKung wrote: > > I always thought that having nullable columns in a table is a Bad > > Thing (http://technet.microsoft.com/en-us/library/ms191178.aspx) and > > Ridiculous. The argument provided in that article is specious and likely SQL > Server-specific. NULLable columns should occur wherever your data model calls > for them, typically when you want to have a marker for "unknown" data. The > advice in that article to move NULLable columns off to a separate table will > actually cause worse, manual "special handling that increases the complexity > of data operations" than the built-in and optimized handling the engine > provides for NULLs. You should ignore this terrible advice. I disagree that it's ridiculous. There are good arguments for avoiding NULLs, not the least of which is that they can lead to very unintuitive results from queries due to 3VL. I think the passage in question (from the above URL) is reasonably good advice. They recommend vertical partitioning to avoid NULLs, and I think that is a very good design strategy in many cases. > > I think its much better to avoid it whenever you have the info but > > when you don't you just have to use the EAV model. > > Also ridiculous. You should never "have to use" the EAV so-called "model". Agreed. > question being described. The difficulty of conceptualizing data structures > as EAV is one of the big strikes against it. The quoted citation evidences Agreed. It has many other strikes as well: for instance, it's difficult to form any kind of meaningful predicate for a relation in an EAV design. Regards, Jeff Davis ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to majordomo@xxxxxxxxxxxxxx so that your message can get through to the mailing list cleanly
