On 21/07/10 15:08, Prometheus Prometheus wrote:
> head -> wall
That's about how I feel about SQL NULLs in general.
They seem like a great idea. A way of representing "unknown" or
"undefined" in a generic, consistent manner.
Or is that "a definite value that means empty or absent" ? Depends on
who you ask, which is the first problem.
Then you get to combining them with anything else in any way. Comparing
row-types or arrays with null entries. Uniqueness. Aggregation/counting.
Conceptual mismatches with the null concept in other languages, where
null/None/nil/undef means "the certain value of nothing or emptiness"
rather than "could be anything or nothing, I dunno" as it does in SQL.
SQL NULL's contradictions often remind me of early formulations of set
theory and their ... issues.
http://en.wikipedia.org/wiki/Russell%27s_paradox
--
Craig Ringer
Tech-related writing: http://soapyfrogs.blogspot.com/