id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 2306 Many-to-many queries very slow on MySQL 3.23.58 anonymous nobody "We have a MySQL 3.23.58 database with about 1000 Room and Photo objects, connected by a many-to-many relationship. Given a room r, asking Django to evaluate r.photos.all() runs an explicit join: {{{ SELECT `kords3_photo`.`id`,`kords3_photo`.`image` FROM `kords3_photo` LEFT OUTER JOIN `kords3_room_photos` AS `m2m_kords3_photo__room` ON `kords3_photo`.`id` = `m2m_kords3_photo__room`.`photo_id` WHERE (`m2m_kords3_photo__room`.`room_id` = 1) ORDER BY `kords3_photo`.`image` ASC }}} which takes around 1 second, when the same query rewritten as an implicit join: {{{ SELECT `kords3_photo`.`id`,`kords3_photo`.`image` FROM `kords3_photo` , `kords3_room_photos` WHERE `kords3_photo`.`id` = `kords3_room_photos`.`photo_id` AND `kords3_room_photos`.`room_id` = 1 ORDER BY `kords3_photo`.`image` ASC }}} would take under a millisecond. " defect closed Database layer (models, ORM) dev normal fixed qs-rf-fixed mir@… freakboy3742@… Accepted 0 0 0 0 0 0