title: product set a column unique without being the primary key
body: <p>I wanna create the following table:</p>
  
  <pre><code>create table product (id bigint not null, product_type varchar(50), product_name varchar(100), available_from TIMESTAMP, available_to TIMESTAMP, primary key (id));
  </code></pre>
  
  <p>My table's key is the 'id'.</p>
  
  <p>when inserting in the table, I wanna that the product_type be unique. </p>
  
  <p>How to do that without setting the product_type the key for my table</p>