寻求帮助 SQLSTATE [HY000] [2002] No such file or directory

问题如下

PDOException in Connector.php line 55:
SQLSTATE[HY000] [2002] No such file or directory

以下是我的程序和配置文件

app/Http/Controllers/TongjiController.php 控制器

<?php                                                                 
namespace App\Http\Controllers;                                       
use App\Tongji;                                                       
class TongjiController extends Controller                             
{                                                               
public function info()                                            
{
return Tongji::mTestCRUD(1);  # DB::select                    
}                                                                 
}                                                                     
?>                                                                    

app/Tongji.php model 文件

<?php                                              
namespace App;                                     
use Illuminate\Database\Eloquent\Model;            
use Illuminate\Support\Facades\DB;                 
class Tongji extends Model                         
{                                                  
static function mTestCRUD($iType=1)            
{                                              
$sSql = '';                                
switch($iType)                             
{                                          
case 1:                                
$sSql = 'SELECT * FROM `student`'; 
break;                             
case 2:                                
$sSql = '';                        
break;                             
case 3:                                
$sSql = '';                        
break;                             
default:                               
$sSql = '';                        
}                                          
return DB::select($sSql);                  
}                                              
}                                                  
?>

config/database.php

'mysql' => [                                                                          
'driver'    => 'mysql',                                                           
'host'      => env('DB_HOST', 'localhost'),                                       
'database'  => env('DB_DATABASE', 'forge'),                                       
'username'  => env('DB_USERNAME', 'forge'),                                       
'password'  => env('DB_PASSWORD', ''),                                            
'charset'   => 'utf8',                                                            
'collation' => 'utf8_unicode_ci',                                                 
'prefix'    => '',                                                                
'strict'    => false,                                                             
'engine'    => null,                                                              
], 

.env

DB_HOST=localhost  
DB_DATABASE=laravel
DB_USERNAME=root   
DB_PASSWORD=