嵌套集指數和性能

Question

我有一些麻煩理解在嵌套集模型上使用哪些索引。查詢是：

SELECT `node`.`id`,(COUNT(parent.id) - 1) AS `depth`,`name` FROM `categories` AS `parent` 
INNER JOIN `categories` AS `node` ON (`node`.`lft` BETWEEN parent.lft AND parent.rgt) 
INNER JOIN `filebank_categories` ON (`node`.`id` = `filebank_categories`.`category_id` AND `filebank_categories`.`filebank_id` = 136) 
INNER JOIN `categories_names` ON (`categories_names`.`category_id` = `node`.`id` AND `categories_names`.`language_id` = 1) 
WHERE `node`.`system_id` = parent.system_id 
GROUP BY node.id 
ORDER BY `node`.`lft` ASC 

該查詢在categories需要用〜350ms的〜5000行。 EXPLAIN給出了這樣的：

 
1 SIMPLE filebank_categories  ref  fk_filebank_categories_categories1,filebank_id   filebank_id 5 const        474 Using where; Using temporary; Using filesort 
1 SIMPLE node     eq_ref PRIMARY,lft,category,cat,lft,rgt,system,id,lft,system PRIMARY  4 filebank_categories.category_id  1  
1 SIMPLE parent     ref  lft,category,system          system  5 node.system_id      50 Using where 
1 SIMPLE categories_names  eq_ref PRIMARY,fk_categories_names_categories1     PRIMARY  8 node.id,const      1 Using where 

表結構：

CREATE TABLE `categories` (
    `id` int(11) NOT NULL AUTO_INCREMENT, 
    `system_id` int(11) DEFAULT NULL, 
    `lft` int(11) DEFAULT NULL, 
    `rgt` int(11) DEFAULT NULL, 
    PRIMARY KEY (`id`), 
    KEY `lft,category` (`lft`,`id`), 
    KEY `cat,lft,rgt` (`id`,`lft`,`rgt`), 
    KEY `system` (`system_id`), 
    CONSTRAINT `categories_ibfk_1` FOREIGN KEY (`system_id`) REFERENCES `systems` (`id`) 
) ENGINE=InnoDB AUTO_INCREMENT=11519 DEFAULT CHARSET=utf8; 

任何想法如何改進呢？它甚至有可能嗎？我在數據庫優化方面並不是很有經驗，因此我無法弄清楚在這裏使用哪些索引（以及爲什麼）。

感謝。

Answer 1

你可以嘗試移動WHERE clause加入，像

SELECT ... 
INNER JOIN `categories` AS `node` ON 
(
    node.system_id=parent.system_id AND 
    node.lft BETWEEN parent.lft AND parent.rgt 
) 

和細化指標爲：

CREATE TABLE `categories` (
    ... 
    KEY `system_id,lft,rgt` (`system_id`,`lft`,`rgt`), 
    ... 
);