title: Does MySQL allow two primary keys on one table?
body: <pre><code>CREATE TABLE Orders
  -&gt; (
  -&gt;    ID SMALLINT UNSIGNED NOT NULL,
  -&gt;    ModelID SMALLINT UNSIGNED NOT NULL,
  -&gt;    Descrip VARCHAR(40),
  -&gt;    PRIMARY KEY (ID, ModelID)
  -&gt; );
  </code></pre>
  
  <p>Basically, this appears to me to be creating two primary key on one table. Is that correct?</p>
  
  <p>I thought that we could create a number of unique keys in one table, but only one primary key.</p>
  
  <p>How is it that my system is allowing the creation of multiple primary keys?</p>
  
  <p>Please advise: what are the rules governing this?</p>