Re: The BOOLEAN data type

>> Well.... SQL has many faults, one of them being the value of having
a
NULL datatype. <<

It is not a datatype! It is not a data value! It is a marker for a missing value. These differences are important.

>> While I tend to agree that nulls in basetables are of little or no
value, I do see the NULL value as a reasonable way to support outer joins. <<

While I want to have DEFAULT or NOT NULL whenever possible, NULLs can be useful in tables. My favorite is as an "eternity symbol" in durations:

 CREATE TABLE Foobar
 (...
  start_date DATE DEFAULT CURRENT_TIMESTAMP NOT NULL,   end_date DATE, -- null means on-going event   CHECK(start_date <= end_date),
 ...);

>> This terrible of treating null-values with propagation is just
incoherent, however. Who ever invented that? <<

Dr. Codd. He later had two nulls -- missing value, and missing attribute

>> While meaningful for e.g. arithmetic values (null + x is clearly
null, and it seems reasonable to treat null*x = null even though this is incoherent if x = 0), <<

Try (null/0); a lot of SQL products got it wrong. You are assuming that a NULL is a value of a numeric datatype, so that the laws of arithemetic apply. It is not a numeric; it has no datatype at all.

>> Why does SQL not use three-valued logic? <<

Dr. Codd and the NULLs required it. Received on Fri Apr 18 2003 - 00:19:00 CEST