Re: Two-valued logic

>> ... And all kinds of ways of dealing with "missing data". Should
the relational model bake in support for all of them, or if not, then which ones, exactly? <<

You ought to be able to do something for missing data; it is a fact of life. Date's tricks for avoiding it just don't work. He had a soluton to an old SQL puzzle of mine on www.dbdebunk.com where we wanted the current salary date and the previous salary, but a new-hire (i.e. no previous data) ws to show up as a NULL. He used an actual date for a missing date (1900-01-01 or something); this implied that there was a loooooong time between raises for some personnel.

Well, the solution we came up in SQL with is the NULL. The advantage is that it has known characteristics, is pretty minimal and has built-in support. The dis-advantage is that missing data depends on the datatype -- those IEEE floating point thingies you just mentioned for numerics, versus strings, versus temporal data (+/- eternity, etc.) Received on Tue Jan 06 2004 - 02:27:40 CET