解决在laravel中auth建立时候遇到的问题

$ php artisan migrate
Migration table created successfully.



 [Illuminate\Database\QueryException]
 SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was t
 oo long; max key length is 767 bytes (SQL: alter table `users` add unique `
 users_email_unique`(`email`))

 [PDOException]
 SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was t
 oo long; max key length is 767 bytes

 [Illuminate\Database\QueryException]
 SQLSTATE[42S01]: Base table or view already exists: 1050 Table 'users' alre
 ady exists (SQL: create table `users` (`id` int unsigned not null auto_incr
 ement primary key, `name` varchar(191) not null, `email` varchar(191) not n
 ull, `password` varchar(191) not null, `remember_token` varchar(100) null,
 `created_at` timestamp null, `updated_at` timestamp null) default character
 set utf8mb4 collate utf8mb4_unicode_ci)

 [PDOException]
 SQLSTATE[42S01]: Base table or view already exists: 1050 Table 'users' alre
 ady exists

use Illuminate\Support\Facades\Schema;
 
/**
 * 引导任何应用程序服务。
 *
 * @return void
 */
public function boot()
{
 Schema::defaultStringLength(191);
}