title: ORA-00904: "BRANCH_ID": invalid identifier
body: <p>Why is the create tables not allowing me to add the staff tables, the CONSTRAINT seem logical to me.</p>
  
  <pre><code>CREATE TABLE branch 
  (
  Branch_ID  VARCHAR(2),
  Branch_Name  VARCHAR(20),
  Branch_Address  VARCHAR(40),
  Branch_Postcode  VARCHAR(15),
  Branch_Telephone NUMBER(15),
  Branch_email VARCHAR(40),
  Branch_Fax NUMBER(15),
  PRIMARY KEY ( Branch_ID )
  );
  
  CREATE TABLE staff
  (
      Staff_ID INT NOT NULL PRIMARY KEY,
      firstName VARCHAR(20),
      lastName VARCHAR(20),
      addressLine_1 VARCHAR2(30),
      city VARCHAR2(15),
      postcode VARCHAR2(7),
      telephone VARCHAR2(15),
      salary DECIMAL (19,4),
      CONSTRAINT BRANCH_fk FOREIGN KEY(Branch_ID ) REFERENCES branch(Branch_ID )
  );
  </code></pre>
  
  <p>ORA-00904: "BRANCH_ID": invalid identifier</p>