Question

I have a table called Address which has a not-null CityID column and a nullable DistrictID column.

I want to make sure that if a district is entered to the table the district is indeed a district of the spesific city. Can I do that with a Check Constraint?

My table structure is as follows:

City: CityID (int), Name(nvarchar)

District: DistrictID (int), CityID (int), Name(nvarchar)

Address: AddressID (int), CityID(int), DistrictID(int)

If it is not doable with a check constraint I would like to see the trigger solution as well.

Answer 1

A composite foreign key containing both cityid and districtid would provide this check.

ALTER TABLE Address
ADD FOREIGN KEY (districtid, cityid) REFERENCES district(districtid, cityid)