Cleanly delete all categories in Magento
If you have been working on a demo store - or yours is still in the early stages of construction, you will probably find it necessary to remove all the categories to start fresh at some point.
Thanks to CasualCommerce, there is a pretty straightforward MySQL "script" to clear out the tables and start fresh.
TRUNCATE TABLE `catalog_category_entity`;
TRUNCATE TABLE `catalog_category_entity_datetime`;
TRUNCATE TABLE `catalog_category_entity_decimal`;
TRUNCATE TABLE `catalog_category_entity_int`;
TRUNCATE TABLE `catalog_category_entity_text`;
TRUNCATE TABLE `catalog_category_entity_varchar`;
TRUNCATE TABLE `catalog_category_product`;
TRUNCATE TABLE `catalog_category_product_index`;
INSERT INTO `catalog_category_entity`(`entity_id`,`entity_type_id`,`attribute_set_id`,`parent_id`,`created_at`,`updated_at`,`path`,`position`,`level`,`children_count`) values (1,3,0,0,'0000-00-00 00:00:00','2009-02-20 00:25:34','1',1,0,1),(2,3,3,0,'2009-02-20 00:25:34','2009-02-20 00:25:34','1/2',1,1,0);
INSERT INTO `catalog_category_entity_int`(`value_id`,`entity_type_id`,`attribute_id`,`store_id`,`entity_id`,`value`) values (1,3,32,0,2,1),(2,3,32,1,2,1);
INSERT INTO `catalog_category_entity_varchar`(`value_id`,`entity_type_id`,`attribute_id`,`store_id`,`entity_id`,`value`) values (1,3,31,0,1,'Root Catalog'),(2,3,33,0,1,'root-catalog'),(3,3,31,0,2,'Default Category'),(4,3,39,0,2,'PRODUCTS'),(5,3,33,0,2,'default-category');