title: How to drop a primary key? I get incorrect table definition
body: <p>I am trying to run this query:</p>
  
  <pre><code>ALTER TABLE table DROP PRIMARY KEY, ADD PRIMARY KEY( `CUSTNO` , `DEPTNO` , `PRODNO` , `DT` );
  </code></pre>
  
  <p>I get</p>
  
  <pre><code>Incorrect table definition; there can be only one auto column and it must be defined as a key
  </code></pre>