Laravel5的数据库表建立问题

我跟着@JellyBool的视频学习。
在CMD命令行上运行了下面的命令。

php artisan make:migration create_articles_table --create=articles

然后在 2015_10_23_022143_create_articles_table.php 中书写了下面的代码

public function up()
    {
        Schema::create('articles', function (Blueprint $table) {
            $table->increments('id');
            $table->string('title');
            $table->text('content');
            $table->timestamps('published_at');
            $table->timestamps();
        });
    }

接着在CMD上运行就弹出错误了，数据库里也没有显示articles表，是哪个地方出现了字段重复？

D:\laravel>php artisan migrate



  [Illuminate\Database\QueryException]
  SQLSTATE[42S21]: Column already exists: 1060 Duplicate column name 'created
  _at' (SQL: create table `articles` (`id` int unsigned not null auto_increme
  nt primary key, `title` varchar(255) not null, `content` text not null, `cr
  eated_at` timestamp default 0 not null, `updated_at` timestamp default 0 no
  t null, `created_at` timestamp default 0 not null, `updated_at` timestamp d
  efault 0 not null) default character set utf8 collate utf8_unicode_ci)






  [PDOException]
  SQLSTATE[42S21]: Column already exists: 1060 Duplicate column name 'created
  _at'

最后解决方法是：

删除所有表，再次执行php artisan migrate

不过我在操作过程中又出现了新的问题

>php artisan migrate


  [Illuminate\Database\QueryException]
  SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 1000 bytes (SQL: alter table `users` add uniqu
  e `users_email_unique`(`email`))

于是，我清空数据表，修改App/Providers/AppServiceProvider.php文件，

添加两行代码，use Illuminate\Support\Facades\Schema;和Schema::defaultStringLength(191);改变字段长度

<?php

namespace App\Providers;

use Illuminate\Support\ServiceProvider;
use Illuminate\Support\Facades\Schema;//添加

class AppServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        Schema::defaultStringLength(191);//添加
    }

    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
        //
    }
}