title: "Incorrect syntax near the keyword 'alter'" when adding foreign key constraint
body: <p>I have these tables :</p>
  
  <pre><code>Employee(Ename, SSN, Bdate, Address, Dnumber)
  Department ( Dname,Dno,Dmgr_SSN(
  Project(Pname, Pnumber, Plocation, Dnum)
  WorksON(SSN,Pnumber,Hours)
  </code></pre>
  
  <p>When I try to use <code>ALTER</code>:</p>
  
  <pre><code>alter  table  Employee 
  add foreign key (Dnumber)
   REFERENCES Department (Dno);
  </code></pre>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>Msg 156, Level 15, State 1, Line 24<br>
    Incorrect syntax near the keyword 'alter'.</p>
  </blockquote>
  
  <p>Note : I write this query under the definition of tables query  </p>