Hello, > Are NULLs considered values for unique constraints on a table?
No. NULL is not evaluated as part of a unique constraint. What you could do is to declare your column as NOT NULL and provide a DEFAULT value/clause for your column, using a value which your application interprets as unknown / unset etc ... -- With regards, Thomas Steinmaurer http://www.upscene.com/ Professional Tools and Services for Firebird FB TraceManager, IB LogManager, Database Health Check, Tuning etc. > > e.g. > > CREATE TABLE blah ( > col1 INT NOT NULL, > col2 INT, > > CONSTRAINT unq_blah UNIQUE(col1, col2) > ); > > INSERT INTO blah (col1, col2) (123, 321); > INSERT INTO blah (col1, col2) (123, 999); /* okay */ > INSERT INTO blah (col1, col2) (123, 321); /* error */ > > INSERT INTO blah (col1, col2) (123, NULL); > INSERT INTO blah (col1, col2) (123, NULL); /* okay? error? */ > > I'd like that NULL example to be an error, does the UNIQUE constraint do > that, or do I have to use a CHECK constraint? If it does require the > CHECK, are there any performance tips for that setup? > > Scott > > > > ------------------------------------ > Posted by: Scott Morgan <bl...@blueyonder.co.uk> > ------------------------------------ > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > Visit http://www.firebirdsql.org and click the Documentation item > on the main (top) menu. Try FAQ and other links from the left-side menu > there. > > Also search the knowledgebases at > http://www.ibphoenix.com/resources/documents/ > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > ------------------------------------ > > Yahoo Groups Links > > >
