On Jul 7, 2006, at 3:57 AM, Malcolm Tredinnick wrote: >> >> Actually, with SQLite at least, it seems that multiple NULL values >> are >> considered non unique.
NULL is not a value, it is the lack of a value. In database theory, you cannot compare one NULL against another NULL or against a value like a string or number, as you can compare 1 with 1, hence you cannot have a unique NULL. This is why SQL has a separate syntax for determining NULL: column IS NULL vs column = 5 I have seen people on database newgroups asking how to sort columns containing NULLs (are they less or greater than any value?). Since you cannot compare NULLs, you cannot sort a table reliably. Each database implementation may return rows containing columns with NULLs in a different though possibly consistent manner. Don --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users -~----------~----~----~----~------~----~------~--~---
