Het punt is dat je de mysql-socket van MAMP in de .env zo moet toewijzen.
DB_SOCKET=/Applications/MAMP/tmp/mysql/mysql.sock
EDIT:ik gebruik laravel 5.8, in eerdere versies moet je de socket rechtstreeks aan de array-verbindingen toevoegen, zoals:
config/database.php
'mysql' => [
'driver' => 'mysql',
'url' => env('DATABASE_URL'),
'host' => env('DB_HOST', '127.0.0.1'),
'port' => env('DB_PORT', '3306'),
'database' => env('DB_DATABASE', 'forge'),
'username' => env('DB_USERNAME', 'forge'),
'password' => env('DB_PASSWORD', ''),
'unix_socket' => '/Applications/MAMP/tmp/mysql/mysql.sock', <----HERE
'charset' => 'utf8mb4',
'collation' => 'utf8mb4_unicode_ci',
'prefix' => '',
'prefix_indexes' => true,
'strict' => true,
'engine' => null,
'options' => extension_loaded('pdo_mysql') ? array_filter([
PDO::MYSQL_ATTR_SSL_CA => env('MYSQL_ATTR_SSL_CA'),
]) : [],
],