console/migrations/m160203_133308_add_field_specialization.php

<?php

use yii\db\Migration;

class m160203_133308_add_field_specialization extends Migration
{
    public function up()
    {
        $this->addColumn('specialization', 'image', $this->string(255));
    }

    public function down()
    {
        $this->dropColumn('specialization', 'image');
    }
}