> Your thoughts? Would it be better to disallow nulls and just use the dummy value with a histogram?

IMHO there are many situations were NULLs are useful. In fact, I think that using “dummy values” like 21-Dec-4000 is really not much better. Hence, the only other possibility is to design the tables to avoid such cases. But, hey, how we would model one (or several) table(s) to store “first name”, “last name” and “middle name” (knowing that the latter might not be available)? Of course I can think of a comple of solutions… But, honestly, I don’t really like them.

In summary, I think that working without NULLs is not the way to go (at least with a database engine like Oracle). That said, the developers must be aware of the problems related to them.

Cheers,
Chris

My problem is that I find them useful in some circumstances. With an effective end date, for example (slowly changing dimensions), is it better to allow nulls (any current record will have an undefined end date?), or to use a dummy value like 31-Dec-4000?

Jonathan Lewis seems to prefer allowing nulls, in p. 124 of CBO Fundamentals, but suggests histograms if nulls aren’t allowed, on p. 178, so seems to allow for avoiding nulls — but the implication is that nulls aren’t a bad thing (at least from a performance perspective).

Your thoughts? Would it be better to disallow nulls and just use the dummy value with a histogram?

Thank you very much for your thoughts! It’s really nice to know that I’m not the only one feeling like that ;-)

Cheers,
Chris

The issue of nulls is much more important. Its a pity that more space was not devoted to the subject, because, ultimately, if nulls are adopted within a relational model (and thus one departs from two-valued logic), the fundamental integrity of the database is compromised. With 2VL, one can demonstrate categorically the integrity of the results obtained from any query. Departing from 2VL, one cannot. Now transpose that uncertainty into a database system providing answers to life-critical systems, like designing aircraft. Need one say more?