title: SQL ORA-02270: no matching unique or primary key for this column-list
body: <p>i'm creating a few tables which look like this</p>
  
  <pre><code>CREATE TABLE sickness
  (
  sickness_id     number(2),
  sickness_name   varchar2(20),
  PRIMARY KEY (sickness_id)
  );
  
  CREATE TABLE cover
  (
  cover_needed char(1) NOT NULL,
  employee_id number(3),
  responsibilities varchar2(50),
  notes varchar2(50),
  PRIMARY KEY (cover_needed, employee_id)
  );
  </code></pre>
  
  <p>this works fine then when i try to make a parent table (see below), i get the error.</p>
  
  <pre><code>ORA-02270: no matching unique or primary key for this column-list
  </code></pre>
  
  <p>i have however narrowed it down to the last line but i can not for the life of me figure it out, thank you </p>
  
  <pre><code>CREATE TABLE absences
  (
  absences_id  number(2) NOT NULL,
  manager_id number(3),
  employee_id number(3) NOT NULL,
  absence_name varchar2(15) NOT NULL,
  sickness_id number(2),
  date_from date NOT NULL,
  date_to date NOT NULL,
  length number(2) NOT NULL,
  description varchar2(40),  
  authorised_by_manager char(1) NOT NULL,
  cover_needed char(1) NOT NULL,
  half_day char(1) NOT NULL,
  
  PRIMARY KEY (absences_id, manager_id, employee_id),
  
  FOREIGN KEY (sickness_id)  REFERENCES sickness (sickness_id),
  FOREIGN KEY (cover_needed) REFERENCES cover    (cover_needed)
  );
  </code></pre>