title: MySQL Auto increment not incrementing
body: <p>I've created a table with 3 columns: postID, userID, and comment.</p>
  
  <p>I have the postID as the primary key, and I am trying to make this auto-increment every time I add a new row to the table.</p>
  
  <pre><code>INSERT INTO CommentTable (postID, userID, comment) VALUES (DEFAULT, "test", "test")
  </code></pre>
  
  <p>When I run this query, it will run OK once but then when I run it again I get "1062 - Duplicate entry '0' for key 'PRIMARY'".</p>
  
  <p>How do I properly set up an auto-increment primary key?</p>
  
  <p>Here is the table structure:</p>
  
  <pre><code>DROP TABLE IF EXISTS `CommentTable`;
  CREATE TABLE `CommentTable` (
    `postID` int(10) NOT NULL,
    `userID` varchar(10) NOT NULL,
    `comment` varchar(1000) DEFAULT NULL,
    PRIMARY KEY (`commentID`)
  ) 
  </code></pre>