title: Laravel migration: fields that defined as interger wil be treated as auto increment?
body: <p>Here is my code:</p>
  
  <pre><code>public function up()
      {
          Schema::create('sysmods', function (Blueprint $table) {
              $table-&gt;increments('mod_id');
              $table-&gt;string('mod_name','60');
              $table-&gt;string('mod_alias_name','60');
              $table-&gt;integer('mod_tb_id','6');// this will become auto increment?
              $table-&gt;timestamps();
          });
      }
  </code></pre>
  
  <p>when i run the migrate command, it says:
  " [PDOException]
   SQLSTATE[42000]: Syntax error or access violation: 1075 Incorrect table def
   inition; there can be only one auto column and it must be defined as a key" </p>
  
  <p>Then as i check the sql, I found this:
       (SQL: create table <code>la_sysmods</code> (<code>mod_id</code> int unsigned not null auto_increm
   ent primary key, <code>mod_name</code> varchar(60) not null, <code>mod_alias_name</code> varchar(
   60) not null, <strong><em><code>mod_tb_id</code> int not null auto_increment primary key</em></strong>, <code>created
   _at</code> timestamp null, <code>updated_at</code> timestamp null) default character set utf
   8 collate utf8_unicode_ci)</p>
  
  <p>The field 'mod_tb_id' which marked as integer has become increments. What's the problem? Thanks!</p>