title: Laravel migration table field's type change
body: <p>Following is my file <em>2015_09_14_051851_create_orders_table.php</em>.
  And I want to change <code>$table-&gt;integer('category_id');</code> as a string with new migration.</p>
  
  <pre><code>&lt;?php
  
  use Illuminate\Database\Schema\Blueprint;
  use Illuminate\Database\Migrations\Migration;
  
  class CreateOrdersTable extends Migration {
  
      /**
       * Run the migrations.
       *
       * @return void
       */
      public function up()
      {
          Schema::create('orders', function(Blueprint $table)
          {
              $table-&gt;increments('id');
              $table-&gt;string('num');
              $table-&gt;integer('user_id');
  
              $table-&gt;text('store_name');
              $table-&gt;integer('store_name_publication');
  
              $table-&gt;string('postal_code', 255);
              $table-&gt;string('phone_number', 255);
  
              $table-&gt;text('title');
              $table-&gt;text('description');
  
              $table-&gt;string('list_image_filename1', 255);
              $table-&gt;string('list_image_filename2', 255)-&gt;nullable();
              $table-&gt;string('list_image_filename3', 255)-&gt;nullable();
              $table-&gt;string('list_image_filename4', 255)-&gt;nullable();
              $table-&gt;string('list_image_filename5', 255)-&gt;nullable();
  
              $table-&gt;integer('term');
  
              $table-&gt;datetime('state0_at')-&gt;nullable();
              $table-&gt;datetime('state1_at')-&gt;nullable();
              $table-&gt;datetime('state2_at')-&gt;nullable();
              $table-&gt;datetime('state3_at')-&gt;nullable();
              $table-&gt;datetime('state4_at')-&gt;nullable();
              $table-&gt;datetime('state5_at')-&gt;nullable();
              $table-&gt;datetime('state6_at')-&gt;nullable();
              $table-&gt;datetime('state7_at')-&gt;nullable();
              $table-&gt;datetime('state8_at')-&gt;nullable();
              $table-&gt;datetime('state9_at')-&gt;nullable();
              $table-&gt;datetime('state10_at')-&gt;nullable();
  
              $table-&gt;integer('category_id');
              $table-&gt;integer('target_customer_sex');
              $table-&gt;integer('target_customer_age');
  
              $table-&gt;integer('payment_order');
              $table-&gt;integer('num_comment');
              $table-&gt;integer('num_view');
              $table-&gt;string('num_pop');
  
              $table-&gt;integer('money');
              $table-&gt;integer('point');
  
              $table-&gt;datetime('closed_at');
              $table-&gt;timestamps();
              $table-&gt;softDeletes();
          });
      }
  
      /**
       * Reverse the migrations.
       *
       * @return void
       */
      public function down()
      {
          Schema::drop('orders');
      }
  
  }
  </code></pre>