Question

i have a table with two foreign keys as composite key.

ActivityTbl –

(activityNbr(PK), supervisor(FK), status, type, startDate, endDate, location )

VolunteerTbl –

(volunteerNbr(PK), name, address, contact)

Now I created a table where volunteer’s choices can be stored as per their prefereance rating.

ActivityChoice

(activityNbr(FK), VolunteerNbr(FK), Rating)

So the combination of those 2 FKs make a composite key. I am using sql Server to create a table.

Create ActivityChoiceTbl(
     VolunteerNbr   int NOT NULL,
     ActivityNbr    int NOT NULL,
     Rank           int NOT NULL,
     CONSTRAINT PKActivityChoice    PRIMARY KEY (VolunteerNbr,ActivityNbr), 
     CONSTRAINT CKRank CHECK (Rank>0 AND Rank<=9));

So in this case do I need to add another foreign key constrain for both to mention that they are foreign keys?? Am I doing it right?? Thanks

Answer 1

Yes, you need two foreign key constraints. The most direct way in standard SQL is to immediately reference the table.

Create ActivityChoiceTbl(
     VolunteerNbr   int NOT NULL REFERENCES VolunteerTbl (volunteerNbr),
     ActivityNbr    int NOT NULL REFERENCES ActivityTbl (activityNbr),
     Rank           int NOT NULL,
     CONSTRAINT PKActivityChoice    PRIMARY KEY (VolunteerNbr,ActivityNbr), 
     CONSTRAINT CKRank CHECK (Rank>0 AND Rank<=9));

But adding two more constraint clauses lets you name the constraints, which is a better practice.

Create ActivityChoiceTbl(
     VolunteerNbr   int NOT NULL,
     ActivityNbr    int NOT NULL,
     Rank           int NOT NULL,
     CONSTRAINT PKActivityChoice    PRIMARY KEY (VolunteerNbr,ActivityNbr), 
     CONSTRAINT FKActivityChoiceVolunteerNbr 
         FOREIGN KEY (VolunteerNbr) REFERENCES VolunteerTbl (VolunteerNbr),
     CONSTRAINT FKActivityChoiceActivityNbr 
         FOREIGN KEY (ActivityNbr) REFERENCES ActivityTbl (ActivityNbr),
     CONSTRAINT CKRank CHECK (Rank>0 AND Rank<=9));

If ActivityChoice is a separate table that needs to reference ActivityChoiceTbl, then you also need something along these lines.

CREATE TABLE ActivityChoice (
    VolunteerNbr INTEGER NOT NULL,
    ActivityNbr INTEGER NOT NULL,
    Rating  DECIMAL (2,1) NOT NULL CHECK (Rating between 0 and 9),  -- Pure guess
    PRIMARY KEY (VolunteerNbr, ActivityNbr),
    FOREIGN KEY (VolunteerNbr, ActivityNbr) 
      REFERENCES ActivityChoiceTbl (VolunteerNbr, ActivityNbr)
);