laravel 表迁移报错[通俗易懂]

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error infomation:

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

  at D:\WWW\test\vendor\laravel\framework\src\Illuminate\Database\Connection.php:664
    660|         // If an exception occurs when attempting to run a query, we'll format the error
    661|         // message to include the bindings with SQL, which will make this exception a
    662|         // lot more helpful to the developer instead of just the database's errors.
    663|         catch (Exception $e) {
  > 664|             throw new QueryException(
    665|                 $query, $this->prepareBindings($bindings), $e
    666|             );
    667|         }
    668|

  Exception trace:

  1   PDOException::("SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 767 bytes")
      D:\WWW\test\vendor\laravel\framework\src\Illuminate\Database\Connection.php:458

  2   PDOStatement::execute()
      D:\WWW\test\vendor\laravel\framework\src\Illuminate\Database\Connection.php:458

  Please use the argument -v to see more details.

解决：
索引长度 & Mysql / MariaDB
Laravel 默认使用 utf8mb4 编码，它支持在数据库中储存 emojis 。如果你是在版本低于 5.7.7 的 MySQL 或者版本低于 10.2.2 的 MariaDB 上创建索引，那你就需要手动配置数据库迁移的默认字符串长度。
即在 AppServiceProvider 中调用 Schema::defaultStringLength 方法来配置它：

use Illuminate\Support\Facades\Schema;

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