Reference to primary key with constraints - sql

Question

I have 2 tables in my database:
CREATE TABLE Apartment
(
StreetName char(50) not null,
Number Integer not null,
Door Integer not null,
Type char(30) not null,
SizeSquareMeter Integer not null,
NID Integer not null FOREIGN KEY REFERENCES Neighborhood(NID)
CONSTRAINT Address PRIMARY KEY (StreetName, Number, Door)
);
CREATE TABLE Resident
(
RID Integer not null PRIMARY KEY,
FirstName varchar(30) not null,
LastName varchar(30) not null,
BirthDate date not null,
Address
);
Now the primary key in apartment is Address and is based on constraint. I want to create a foreign key Address in the Resident table referencing the
primary key Address in the Apartment table.
How can I do that?

Answer 1

Since your primary key in Apartment is made up from three columns, any table wanting to reference Apartment will also need to have ALL three columns to establish a foreign key link.
So you need to change your Resident table to:
CREATE TABLE Resident
(
RID Integer not null PRIMARY KEY,
FirstName varchar(30) not null,
LastName varchar(30) not null,
BirthDate date not null,
StreetName char(50) not null,
Number Integer not null,
Door Integer not null,
);
and then you can add the foreign key constraint:
ALTER TABLE Resident
ADD CONSTRAINT FK_Resident_Apartment
FOREIGN KEY (StreetName, Number, Door) REFERENCES Apartment (StreetName, Number, Door);
The other option would be to add a surrogate column (an artificial, additional column) to Apartment - either as primary key, or (for SQL Server) at least with a unique constraint - so that you could establish the FK link to that surrogate column (using that one, single column - instead of having to replicate three columns of "real" data)