Add unique - Migration

add_constraint_mytable.php

<?php

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

class AddConstraintMyTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('myTable', function (Blueprint $table) {
           $table->unique('link');
           $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::table('myTable', function (Blueprint $table) {
            $table->dropUnique('offers_link_unique');
        });
    }
}