I\'ve trying to import a products list to magento. In the firsts test, I got success, but the products were not showing up in back or front office.
After redo the impor
Delete products with a SQL query is not the Magento way and I recommend not doing it. It may cause database corruption or problems with the foreign key indexes/constraints as stated here.
Everybody interested in using a correct, safe and also fast way to alter things in Magento should ALWAYS use Magento's ORM functions.
In this case this would be in a php script.
Mage::getModel('catalog/product')->getCollection()->delete();
This is the only safe way in Magento.