Works on prestashop 1.6
How to apply same tax rule on all products quickly
UPDATE ps_product SET id_tax_rules_group = 1 WHERE id_tax_rules_group = 0; UPDATE ps_product_shop SET id_tax_rules_group = 1 WHERE id_tax_rules_group = 0;
Making a mass price change
UPDATE ps_product_shop SET price = 10; UPDATE ps_product SET price = 10;