1.配置.env 文件

DB_HOST=host
DB_DATABASE=database
DB_USERNAME=username
DB_PASSWORD=password

OTHER_DB_HOST=host
OTHER_DB_DATABASE=database
OTHER_DB_USERNAME=username
OTHER_DB_PASSWORD=password

2.修改 database.php 文件
在 connections 中 mysql 的下面添加

'mysql_other' => [
    'driver'    => 'mysql',
    'host'      => env('OTHER_DB_HOST', 'localhost'),
    'database'  => env('OTHER_DB_DATABASE', 'forge'),
    'username'  => env('OTHER_DB_USERNAME', 'forge'),
    'password'  => env('OTHER_DB_PASSWORD', ''),
    'charset'   => 'utf8',
    'collation' => 'utf8_unicode_ci',
    'prefix'    => '',
    'strict'    => false,
    'engine'    => null,
],

3.在 model 中使用

class Message extends Model
{
    protected $connection = 'mysql_other';
}

4.在查询构造器中使用

$results = DB::connection('mysql_other')->select('...');