alevel_project/database/migrations/2018_04_15_165539_create_items_exchange_table.php

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreateItemsExchangeTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('items_exchange', function (Blueprint $table) {
            $table->increments('id');
            $table->unsignedInteger('item_id');
            $table->unsignedInteger('item_offer_id');
            $table->tinyInteger('status')->default(null)->nullable();
            $table->timestamps();

            $table->foreign('item_id')
                ->references('id')->on('items')
                ->onDelete('cascade');
            $table->foreign('item_offer_id')
                ->references('id')->on('items')
                ->onDelete('cascade');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::table('items_exchange', function (Blueprint $table) {
            $table->dropForeign(['item_id']);
            $table->dropForeign(['item_offer_id']);
        });

        Schema::dropIfExists('items_exchange');
    }
}