Magento used ORM structure for developing e-commerce website so it's faster and easier to fetch and manage data from database. so Magento also stores some unnecessary data which is not much useful for store so you can remove that from the database. Here to display the SQL queries that run in your mysql database. It's only remove junk data not effects on the site..
Here below also provide some other SQL queries for deleting products, orders and users. In below all examples use Magento database without any table prefix.If your database table has any prefix than writes table query as prefix..
Remove Magento junk and unnecessary data from Database
SET FOREIGN_KEY_CHECKS = 0; //Use for ignore foreign key if any.
-- Compare
TRUNCATE `catalog_compare_item`;
-- Wishlist
TRUNCATE `wishlist_item_option`;
TRUNCATE `wishlist_item`;
TRUNCATE `wishlist`;
-- Admin notification
TRUNCATE `adminnotification_inbox`;
-- Dataflow
TRUNCATE `dataflow_batch_export`;
TRUNCATE `dataflow_batch_import`;
-- Report
TRUNCATE `report_event`;
TRUNCATE `report_viewed_product_index`;
TRUNCATE `report_compared_product_index`;
-- Search
TRUNCATE `catalogsearch_fulltext`;
TRUNCATE `catalogsearch_query`;
TRUNCATE `catalogsearch_result`;
-- FLAT CATALOG (EDIT TABLE NAMES)
TRUNCATE `catalog_category_flat_store_1`;
TRUNCATE `catalog_product_flat_1`;
-- Logs
TRUNCATE `log_customer`;
TRUNCATE `log_quote`;
TRUNCATE `log_summary`;
TRUNCATE `log_summary_type`;
TRUNCATE `log_url`;
TRUNCATE `log_url_info`;
TRUNCATE `log_visitor`;
TRUNCATE `log_visitor_info`;
TRUNCATE `log_visitor_online`;
-- Session
TRUNCATE `core_session`;
TRUNCATE `api_session`;
-- Cache
TRUNCATE `core_cache`;
TRUNCATE `core_cache_option`;
TRUNCATE `core_cache_tag`;
-- Index
TRUNCATE `index_event`;
TRUNCATE `index_process_event`;
-- Captcha
TRUNCATE `captcha_log`;
-- Sent to friend
TRUNCATE `sendfriend_log`;
-- Temp and index tables
TRUNCATE `catalog_category_anc_categs_index_tmp`;
TRUNCATE `catalog_category_anc_products_index_tmp`;
TRUNCATE `catalog_category_product_index_enbl_tmp`;
TRUNCATE `catalog_product_index_eav_decimal_tmp`;
TRUNCATE `catalog_product_index_eav_tmp`;
TRUNCATE `catalog_product_index_price_bundle_opt_tmp`;
TRUNCATE `catalog_product_index_price_bundle_sel_tmp`;
TRUNCATE `catalog_product_index_price_bundle_tmp`;
TRUNCATE `catalog_product_index_price_cfg_opt_agr_tmp`;
TRUNCATE `catalog_product_index_price_cfg_opt_tmp`;
TRUNCATE `catalog_product_index_price_downlod_tmp`;
TRUNCATE `catalog_product_index_price_final_tmp`;
TRUNCATE `catalog_product_index_price_opt_agr_tmp`;
TRUNCATE `catalog_product_index_price_opt_tmp`;
TRUNCATE `catalog_product_index_price_tmp`;
TRUNCATE `cataloginventory_stock_status_tmp`;
TRUNCATE `catalog_category_anc_categs_index_idx`;
TRUNCATE `catalog_category_anc_products_index_idx`;
TRUNCATE `catalog_category_product_index_enbl_idx`;
TRUNCATE `catalog_category_product_index_idx`;
TRUNCATE `catalog_product_index_eav_decimal_idx`;
TRUNCATE `catalog_product_index_eav_idx`;
TRUNCATE `catalog_product_index_price_bundle_idx`;
TRUNCATE `catalog_product_index_price_bundle_opt_idx`;
TRUNCATE `catalog_product_index_price_bundle_sel_idx`;
TRUNCATE `catalog_product_index_price_cfg_opt_agr_idx`;
TRUNCATE `catalog_product_index_price_cfg_opt_idx`;
TRUNCATE `catalog_product_index_price_downlod_idx`;
TRUNCATE `catalog_product_index_price_final_idx`;
TRUNCATE `catalog_product_index_price_idx`;
TRUNCATE `catalog_product_index_price_opt_agr_idx`;
TRUNCATE `catalog_product_index_price_opt_idx`;
TRUNCATE `cataloginventory_stock_status_idx`;
SET FOREIGN_KEY_CHECKS = 1;
Remove Magento all 'Products' from Database
SET FOREIGN_KEY_CHECKS = 0;
TRUNCATE TABLE `catalog_product_bundle_option`;
TRUNCATE TABLE `catalog_product_bundle_option_value`;
TRUNCATE TABLE `catalog_product_bundle_selection`;
TRUNCATE TABLE `catalog_product_entity_datetime`;
TRUNCATE TABLE `catalog_product_entity_decimal`;
TRUNCATE TABLE `catalog_product_entity_gallery`;
TRUNCATE TABLE `catalog_product_entity_int`;
TRUNCATE TABLE `catalog_product_entity_media_gallery`;
TRUNCATE TABLE `catalog_product_entity_media_gallery_value`;
TRUNCATE TABLE `catalog_product_entity_text`;
TRUNCATE TABLE `catalog_product_entity_tier_price`;
TRUNCATE TABLE `catalog_product_entity_varchar`;
TRUNCATE TABLE `catalog_product_link`;
TRUNCATE TABLE `catalog_product_link_attribute`;
TRUNCATE TABLE `catalog_product_link_attribute_decimal`;
TRUNCATE TABLE `catalog_product_link_attribute_int`;
TRUNCATE TABLE `catalog_product_link_attribute_varchar`;
TRUNCATE TABLE `catalog_product_link_type`;
TRUNCATE TABLE `catalog_product_option`;
TRUNCATE TABLE `catalog_product_option_price`;
TRUNCATE TABLE `catalog_product_option_title`;
TRUNCATE TABLE `catalog_product_option_type_price`;
TRUNCATE TABLE `catalog_product_option_type_title`;
TRUNCATE TABLE `catalog_product_option_type_value`;
TRUNCATE TABLE `catalog_product_super_attribute_label`;
TRUNCATE TABLE `catalog_product_super_attribute_pricing`;
TRUNCATE TABLE `catalog_product_super_attribute`;
TRUNCATE TABLE `catalog_product_super_link`;
TRUNCATE TABLE `catalog_product_enabled_index`;
TRUNCATE TABLE `catalog_product_website`;
TRUNCATE TABLE `catalog_category_product_index`;
TRUNCATE TABLE `catalog_category_product`;
TRUNCATE TABLE `cataloginventory_stock_item`;
TRUNCATE TABLE `cataloginventory_stock_status`;
TRUNCATE TABLE `cataloginventory_stock`;
TRUNCATE TABLE `rating_option_vote`;
TRUNCATE TABLE `rating_option_vote_aggregated`;
TRUNCATE TABLE `review`;
TRUNCATE TABLE `review_detail`;
TRUNCATE TABLE `review_entity_summary`;
TRUNCATE TABLE `review_store`;
INSERT INTO `catalog_product_link_type`(`link_type_id`,`code`) VALUES (1,'relation'),(2,'bundle'),(3,'super'),(4,'up_sell'),(5,'cross_sell');
INSERT INTO `catalog_product_link_attribute`(`product_link_attribute_id`,`link_type_id`,`product_link_attribute_code`,`data_type`) VALUES (1,2,'qty','decimal'),(2,1,'position','int'),(3,4,'position','int'),(4,5,'position','int'),(6,1,'qty','decimal'),(7,3,'position','int'),(8,3,'qty','decimal');
INSERT INTO `cataloginventory_stock`(`stock_id`,`stock_name`) VALUES (1,'Default');
TRUNCATE TABLE `catalog_product_entity`;
SET FOREIGN_KEY_CHECKS = 1;
Remove Magento all 'Categories' from Database
SET FOREIGN_KEY_CHECKS = 0;
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');
SET FOREIGN_KEY_CHECKS = 1;
Remove Magento all 'Customers' from Database
SET FOREIGN_KEY_CHECKS = 0;
TRUNCATE `customer_address_entity`;
TRUNCATE `customer_address_entity_datetime`;
TRUNCATE `customer_address_entity_decimal`;
TRUNCATE `customer_address_entity_int`;
TRUNCATE `customer_address_entity_text`;
TRUNCATE `customer_address_entity_varchar`;
TRUNCATE `customer_entity`;
TRUNCATE `customer_entity_datetime`;
TRUNCATE `customer_entity_decimal`;
TRUNCATE `customer_entity_int`;
TRUNCATE `customer_entity_text`;
TRUNCATE `customer_entity_varchar`;
SET FOREIGN_KEY_CHECKS = 1;
Remove Magento all 'Orders' from Database
SET FOREIGN_KEY_CHECKS = 0;
TRUNCATE `sales_order`;
TRUNCATE `sales_order_datetime`;
TRUNCATE `sales_order_decimal`;
TRUNCATE `sales_order_entity`;
TRUNCATE `sales_order_entity_datetime`;
TRUNCATE `sales_order_entity_decimal`;
TRUNCATE `sales_order_entity_int`;
TRUNCATE `sales_order_entity_text`;
TRUNCATE `sales_order_entity_varchar`;
TRUNCATE `sales_order_int`;
TRUNCATE `sales_order_text`;
TRUNCATE `sales_order_varchar`;
TRUNCATE `sales_flat_quote`;
TRUNCATE `sales_flat_quote_address`;
TRUNCATE `sales_flat_quote_address_item`;
TRUNCATE `sales_flat_quote_item`;
TRUNCATE `sales_flat_quote_item_option`;
TRUNCATE `sales_flat_order_item`;
SET FOREIGN_KEY_CHECKS = 1;
