$table->index in laravel code example
Example 1: laravel migration foreign key 5.6
Schema::table('posts', function (Blueprint $table) {
$table->unsignedInteger('user_id');
$table->foreign('user_id')->references('id')->on('users');
});
Example 2: laravel create migration
php artisan make:migration add_votes_to_users_table --table=users
php artisan make:migration create_users_table --create=users