links-to-marketplaces/upload/admin/model/extension/module/links_to_marketplaces.php

<?php
class ModelExtensionModuleLinksToMarketplaces extends Model {
    public function addColumnsToTable() {
        $has_url_ozon_column = $this->db->query("SHOW COLUMNS FROM " . DB_PREFIX . "product WHERE Field='url_ozon'")->num_rows > 0;

        if (!$has_url_ozon_column) {
            $this->db->query("ALTER TABLE " . DB_PREFIX . "product ADD COLUMN url_ozon VARCHAR(255) NULL");
        }

        $has_url_wildberries_column = $this->db->query("SHOW COLUMNS FROM " . DB_PREFIX . "product WHERE Field='url_wildberries'")->num_rows > 0;

        if (!$has_url_wildberries_column) {
            $this->db->query("ALTER TABLE " . DB_PREFIX . "product ADD COLUMN url_wildberries VARCHAR(255) NULL");
        }

        $has_url_yandex_market_column = $this->db->query("SHOW COLUMNS FROM " . DB_PREFIX . "product WHERE Field='url_yandex_market'")->num_rows > 0;

        if (!$has_url_yandex_market_column) {
            $this->db->query("ALTER TABLE " . DB_PREFIX . "product ADD COLUMN url_yandex_market VARCHAR(255) NULL");
        }

        $has_url_megamarket_column = $this->db->query("SHOW COLUMNS FROM " . DB_PREFIX . "product WHERE Field='url_megamarket'")->num_rows > 0;

        if (!$has_url_megamarket_column) {
            $this->db->query("ALTER TABLE " . DB_PREFIX . "product ADD COLUMN url_megamarket VARCHAR(255) NULL");
        }
    }
}