Hi,

How common is it to change the FK constraint that would ignore empty records. Here is an example of FK:

ALTER TABLE [dbo].[eq_file]  WITH CHECK ADD CONSTRAINT [FK_eq_file_site_category] FOREIGN KEY([SITE_NO],[category])
	REFERENCES [dbo].[calpmcat] ([SITE_NO],[CATEGORY])
	ON UPDATE CASCADE
	ON DELETE SET DEFAULT

The problem with the above is that table EQ_FILE could have any number of records where the field CATEGORY is empty string. Which means that the CALPMCAT has to have a record with empty CATEGORY for every SITE_NO that exists. Which does not make sense to me.
And the only way I see to get around it is to change the above expression to ignore records with empty CATEGORY.
My questions:
1. How do you modify the expression to ignore empty field?
2. Is this a good/common practice?

TIA