i have such 3 tables. Im trying to Left Join them
SELECT `t`.`title` AS `category_title`,`t`.`id` AS `category_id`, `st`.`title` AS
`subcategory_title`, `st`.`id` AS `subcategory_id`, `st`.`parent_id` AS
`subcategory_parent`, `n`.`title` AS `news_title`,`n`.`id` AS `news_id` FROM
`t_categories` `t` LEFT JOIN t_categories AS `st` ON `st`.`parent_id`=t.`id` LEFT JOIN
t_newsrelations AS `nr` ON `nr`.`category_id`=st.`id` LEFT JOIN t_news AS `n` ON
`n`.`id`=nr.`news_id` WHERE `t`.`enabled` = 1 AND `n`.`enabled` = 1 AND `n`.`type`!=1 AND
`n`.`type`!=5 ORDER BY `t`.`position`,`st`.`position`,`n`.`position` ASC
here is the structure of tables
CREATE TABLE IF NOT EXISTS `t_categories` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`parent_id` int(11) NOT NULL,
`title` tinytext NOT NULL,
`position` tinyint(4) unsigned NOT NULL DEFAULT '0',
`type` tinyint(1) unsigned NOT NULL,
`enabled` tinyint(1) unsigned NOT NULL DEFAULT '1',
UNIQUE KEY `id` (`id`),
KEY `type` (`type`),
KEY `parent_id` (`parent_id`),
KEY `enabled` (`enabled`),
KEY `id_parent_position_enabled` (`id`,`parent_id`,`position`,`enabled`),
KEY `position` (`position`),
KEY `parent_id_2` (`parent_id`,`enabled`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 ;
CREATE TABLE IF NOT EXISTS `t_news` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`title` tinytext NOT NULL,
`m_title` tinytext NOT NULL,
`url` varchar(2000) NOT NULL,
`keywords` text NOT NULL,
`description` text NOT NULL,
`body` longtext NOT NULL,
`position` tinyint(4) unsigned NOT NULL DEFAULT '0',
`type` tinyint(1) unsigned NOT NULL,
`city_id` int(4) NOT NULL,
`quickmenu_enabled` tinyint(1) unsigned NOT NULL DEFAULT '0',
`quickmenu` text NOT NULL,
`enabled` tinyint(1) unsigned NOT NULL DEFAULT '1',
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`),
KEY `position` (`position`),
KEY `type` (`type`),
KEY `city_id` (`city_id`),
KEY `url` (`url`(333)),
KEY `quickmenu_enabled` (`quickmenu_enabled`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 ;
CREATE TABLE IF NOT EXISTS `t_newsrelations` (
`category_id` int(11) NOT NULL,
`news_id` int(11) unsigned NOT NULL,
KEY `category_id` (`category_id`),
KEY `news_id` (`news_id`),
KEY `category_id_2` (`category_id`,`news_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
And SELECT EXPLAIN shows me
t_newsrelations
is intermediate table. Table t_categories
contains categories and subcategories linked by parent_id column. Each item from t_news can be a member of more than one subcategories thats why they linked through t_newsrelations
how to optimise a query? Why it shows Using index, Using temporary, Using filesort?