title: Incorrect syntax near the keyword 'CONSTRAINT'
body: <p>I am getting this error message ...</p>
  
  <blockquote>
    <p>Msg 156, Level 15, State 1, Line 20<br>
     Incorrect syntax near the keyword 'CONSTRAINT'.</p>
  </blockquote>
  
  <p>I've done my research and I'm still stuck on completing this script. </p>
  
  <p>Here`s what I entered.</p>
  
  <pre><code>DROP TABLE SEMESTER; 
  DROP TABLE CLASS;
  DROP TABLE STUDENT;
  
  CREATE TABLE STUDENT (
  stuid int not null,
  stulname CHAR(40) not null,
  stufname CHAR(40) not null,
  stugender CHAR(1) not null,
  stubirthdate DATE not null);
  
  CREATE TABLE CLASS (
  title CHAR(40) not null PRIMARY KEY,
  instructor CHAR(40) not null );
  
  CREATE TABLE SEMESTER (
  year int not null ); 
  
  
  CONSTRAINT pk_student PRIMARY KEY (stuid, stulname, stufname, stugender, stubirthdate),
  CONSTRAINT pk_class PRIMARY KEY (title, instructor),
  CONSTRAINT pk_semester PRIMARY KEY (semid, year)); 
  </code></pre>