(Undefined index: driver) Why I am obtaining this error message when I try to perform a database query on a Laravel application?

I am pretty new in Laravel and I have the following doubt about how to correctly configure the database connection.

I am using Laravel 5.4 and I need to connect to an existing MySql database. So following this tutorial: http://ift.tt/2mi84Qo

I have setted my config/database.php file in this way:

<?php

return [

    /*
    |--------------------------------------------------------------------------
    | Default Database Connection Name
    |--------------------------------------------------------------------------
    |
    | Here you may specify which of the database connections below you wish
    | to use as your default connection for all database work. Of course
    | you may use many connections at once using the Database library.
    |
    */

    //'default' => env('DB_CONNECTION', 'mysql'),

    /*
    |--------------------------------------------------------------------------
    | Database Connections
    |--------------------------------------------------------------------------
    |
    | Here are each of the database connections setup for your application.
    | Of course, examples of configuring each database platform that is
    | supported by Laravel is shown below to make development simple.
    |
    |
    | All database work in Laravel is done through the PHP PDO facilities
    | so make sure you have the driver for your particular database of
    | choice installed on your machine before you begin development.
    |
    */

    'connections' => [

        /*
        'sqlite' => [
            'driver' => 'sqlite',
            'database' => env('DB_DATABASE', database_path('database.sqlite')),
            'prefix' => '',
        ],
        */

        'mysql' => [
            'driver' => 'mysql',
            'host' => env('DB_HOST', '127.0.0.1'),
            'port' => env('DB_PORT', '3306'),
            'database' => env('DB_DATABASE', 'pandaok'),
            'username' => env('DB_USERNAME', 'root'),
            'password' => env('DB_PASSWORD', ''),
            'charset' => 'utf8mb4',
            'collation' => 'utf8mb4_unicode_ci',
            'prefix' => '',
            'strict' => true,
            'engine' => null,
        ],

        /*
        'pgsql' => [
            'driver' => 'pgsql',
            'host' => env('DB_HOST', '127.0.0.1'),
            'port' => env('DB_PORT', '5432'),
            'database' => env('DB_DATABASE', 'forge'),
            'username' => env('DB_USERNAME', 'forge'),
            'password' => env('DB_PASSWORD', ''),
            'charset' => 'utf8',
            'prefix' => '',
            'schema' => 'public',
            'sslmode' => 'prefer',
        ],
        */

    ],

    /*
    |--------------------------------------------------------------------------
    | Migration Repository Table
    |--------------------------------------------------------------------------
    |
    | This table keeps track of all the migrations that have already run for
    | your application. Using this information, we can determine which of
    | the migrations on disk haven't actually been run in the database.
    |
    */

    'migrations' => 'migrations',

    /*
    |--------------------------------------------------------------------------
    | Redis Databases
    |--------------------------------------------------------------------------
    |
    | Redis is an open source, fast, and advanced key-value store that also
    | provides a richer set of commands than a typical key-value systems
    | such as APC or Memcached. Laravel makes it easy to dig right in.
    |
    */

    /*
    'redis' => [

        'client' => 'predis',

        'default' => [
            'host' => env('REDIS_HOST', '127.0.0.1'),
            'password' => env('REDIS_PASSWORD', null),
            'port' => env('REDIS_PORT', 6379),
            'database' => 0,
        ],

    ],
    */

];

As you can see in the previous code snippet I comment all except the settings related to MySql.

I commented also this line:

'default' => env('DB_CONNECTION', 'mysql'),

to avoid that it takes the connection parameter from the .env files that contains:

DB_CONNECTION=mysql
DB_HOST=127.0.0.1
DB_PORT=3306
DB_DATABASE=homestead
DB_USERNAME=homestead
DB_PASSWORD=secret

But doing in this way I am obtaining this error message when I perform this query into a class $resut = DB::select('select * from pm_user where id = ?', [1]);:

ErrorException in DatabaseManager.php line 112:
Undefined index: driver
in DatabaseManager.php line 112
at HandleExceptions->handleError(8, 'Undefined index: driver', 'C:\\xampp\\htdocs\\HotelRegistration\\vendor\\laravel\\framework\\src\\Illuminate\\Database\\DatabaseManager.php', 112, array('name' => null, 'config' => array('mysql' => array('driver' => 'mysql', 'host' => '127.0.0.1', 'port' => '3306', 'database' => 'homestead', 'username' => 'homestead', 'password' => 'secret', 'charset' => 'utf8mb4', 'collation' => 'utf8mb4_unicode_ci', 'prefix' => '', 'strict' => true, 'engine' => null)))) in DatabaseManager.php line 112
at DatabaseManager->makeConnection(null) in DatabaseManager.php line 71
at DatabaseManager->connection() in DatabaseManager.php line 322
at DatabaseManager->__call('select', array('select * from pm_user where id = ?', array(1))) in Facade.php line 221
at DatabaseManager->select('select * from pm_user where id = ?', array(1)) in Facade.php line 221
..............................................................................
..............................................................................
..............................................................................

Why? What is wrong? What am I missing? How can I fix this issue?

And why Laravel defines the database connection parameters in 2 different places (the config/database.php file and the .env file)?

via Chebli Mohamed