When defining a foreign key in this Oracle example, what is the significance of the CONSTRAINT keyword? In the code below, The first column I create for the table courses is a column called department_code. I then define fk_courses_department_code and specify that department_code in this table will be a foreign key that will reference department_code from the departments table. What is the relevance, or significance of the CONSTRAINT fk_courses_department_code line? As far as I'm concerned, it is understood that department_code is a foreign key in this table. What exactly is the role of fk_courses_department_code then? Does it even exist as a real column? Is it just an alias for department_code? What is it, exactly?

CREATE TABLE courses
(
  department_code    VARCHAR2(2)   NOT NULL,
  course_number      NUMBER(3,0)   NOT NULL,
  course_title       VARCHAR2(64)  NOT NULL,
  course_description VARCHAR2(512) NOT NULL,
  credits            NUMBER(3,1)   NOT NULL,
  CONSTRAINT pk_courses
    PRIMARY KEY (department_code, course_number),
  CONSTRAINT fk_courses_department_code
      FOREIGN KEY (department_code)
      REFERENCES departments (department_code),
);
What exactly is the role of fk_courses_department_code then?


It is the name of the constraint. 

This is useful to e.g. drop the constraint later, as that can only be done by supplying the name.