Laravel雄辩的LEFT JOIN WHERe NULL

可以通过指定特定表中所需的特定列名来解决，如下所示：

$c = Customer::leftJoin('orders', function($join) {      $join->on('customers.id', '=', 'orders.customer_id');    })    ->whereNull('orders.customer_id')    ->first([        'customers.id',        'customers.first_name',        'customers.last_name',        'customers.email',        'customers.phone',        'customers.address1',        'customers.address2',        'customers.city',        'customers.state',        'customers.county',        'customers.district',        'customers.postal_pre',        'customers.country'    ]);