Re: Warning about null and open question to Oracle

I suggest you read anything at all by Chris Date about why 3-valued logic is a bastardisation of relational theory.

One of the most understandable arguments he puts forward concerns your proposition that unknown = unknown and therefore NULL = NULL. What makes you think NULL always means unknown? The classic example is in the traditional (employee_id,salary,commision) table. If the employee is a salesman and commission is NULL, that will probably mean that the commision is unknown. If the employee is not a salesman, then the NULL means 'not applicable'.

You might do well to review your database design to eliminate the need for nulls.

PS - I realise that this post may spark an argument about the pros and cons of three-valued (or n-valued) logic...

Henry Harrison
hharriso_at_dircon.co.uk Received on Wed Jun 14 1995 - 00:00:00 CEST