Re: Unique constraint and NULL values

"Agoston Bejo" <gusz1_at_freemail.hu> wrote in message news:cl8ba7$d04$1_at_news.caesar.elte.hu...
| I want to enforce such a constraint on a column that would ensure that the
| values be all unique, but this wouldn't apply to NULL values. (I.e. there
| may be more than one NULL value in the column.)
| How can I achieve this?
| I suppose I would get the most-hated "table/view is changing,
| trigger/function may not see it" error if I tried to write a trigger that
| checks the uniqueness of non-null values upon insert/update.
|
|

did you try a standard UNIQUE constraint on the column?

unlike SQL-Server (unless they've changed it since I last worked on it), Oracle processes null values properly in this scenario (i.e., one NULL value is never consider equal to another NULL value)

++ mcs Received on Thu Oct 21 2004 - 15:37:42 CEST