Change Magento attribute type

gistfile1.sql

INSERT INTO catalog_product_entity_text (`attribute_id`, `entity_id`, `entity_type_id`, `store_id`, `value`)
SELECT ev.`attribute_id`, ev.`entity_id`, ev.`entity_type_id`, ev.`store_id`, ev.`value`
FROM catalog_product_entity_varchar AS ev WHERE ev.`attribute_id` = ATTRIBUTE_ID; 
UPDATE `eav_attribute` SET `backend_type`='text' WHERE `attribute_code`='ATTRIBUTE_CODE';
DELETE FROM catalog_product_entity_varchar WHERE `attribute_id` = ATTRIBUTE_ID;