使用試驗和錯誤我發現,從下面的查詢中刪除連接時,它運行速度快30倍。有人可以解釋爲什麼會這樣,並且如果可以優化查詢以包含沒有性能影響的額外連接。使用昂貴的INNER JOIN優化MySQL查詢
這是解釋的屏幕截圖,它顯示索引未被用於uesr_groups表。
這是原始查詢:
SELECT `comments`.`comment_id`, `comments`.`comment_html`, `comments`.`comment_time_added`, `comments`.`comment_has_attachments`, `users`.`user_name`, `users`.`user_id`, `users`.`user_comments_count`, `users`.`user_time_registered`, `users`.`user_time_last_active`, `user_profile`.`user_avatar`, `user_profile`.`user_signature_html`, `user_groups`.`user_group_icon`, `user_groups`.`user_group_name`
FROM (`comments`)
INNER JOIN `users` ON `comments`.`comment_user_id` = `users`.`user_id`
INNER JOIN `user_profile` ON `users`.`user_id` = `user_profile`.`user_id`
INNER JOIN `user_groups` ON `users`.`user_group_id` = `user_groups`.`user_group_id`
WHERE `comments`.`comment_enabled` = 1
AND `comments`.`comment_content_id` = 12
ORDER BY `comments`.`comment_time_added` ASC
LIMIT 20
如果我刪除 「user_groups」 加入,則查詢運行快30倍,如上所述。
SELECT `comments`.`comment_id`, `comments`.`comment_html`, `comments`.`comment_time_added`, `comments`.`comment_has_attachments`, `users`.`user_name`, `users`.`user_id`, `users`.`user_comments_count`, `users`.`user_time_registered`, `users`.`user_time_last_active`, `user_profile`.`user_avatar`, `user_profile`.`user_signature_html`
FROM (`comments`)
INNER JOIN `users` ON `comments`.`comment_user_id` = `users`.`user_id`
INNER JOIN `user_profile` ON `users`.`user_id` = `user_profile`.`user_id`
WHERE `comments`.`comment_enabled` = 1
AND `comments`.`comment_content_id` = 12
ORDER BY `comments`.`comment_time_added` ASC
LIMIT 20
我的表是下面,任何人都可以提供任何深入瞭解如何避免包括user_groups表性能的下降?
--
-- Table structure for table `comments`
--
CREATE TABLE IF NOT EXISTS `comments` (
`comment_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`comment_content_id` int(10) unsigned NOT NULL,
`comment_user_id` mediumint(6) unsigned NOT NULL,
`comment_original` text NOT NULL,
`comment_html` text NOT NULL,
`comment_time_added` int(10) unsigned NOT NULL,
`comment_time_updated` int(10) unsigned NOT NULL,
`comment_enabled` tinyint(1) NOT NULL DEFAULT '0',
`comment_is_spam` tinyint(1) NOT NULL DEFAULT '0',
`comment_has_attachments` tinyint(1) unsigned NOT NULL,
`comment_has_edits` tinyint(1) NOT NULL,
PRIMARY KEY (`comment_id`),
KEY `comment_user_id` (`comment_user_id`),
KEY `comment_content_id` (`comment_content_id`),
KEY `comment_is_spam` (`comment_is_spam`),
KEY `comment_enabled` (`comment_enabled`),
KEY `comment_time_updated` (`comment_time_updated`),
KEY `comment_time_added` (`comment_time_added`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=352 ;
-- --------------------------------------------------------
--
-- Table structure for table `users`
--
CREATE TABLE IF NOT EXISTS `users` (
`user_id` mediumint(6) unsigned NOT NULL AUTO_INCREMENT,
`user_ipb_id` int(10) unsigned DEFAULT NULL,
`user_activated` tinyint(1) NOT NULL DEFAULT '0',
`user_name` varchar(64) CHARACTER SET latin1 NOT NULL,
`user_email` varchar(255) NOT NULL,
`user_password` varchar(40) NOT NULL,
`user_content_count` int(10) unsigned NOT NULL DEFAULT '0',
`user_comments_count` int(10) unsigned NOT NULL DEFAULT '0',
`user_salt` varchar(8) NOT NULL,
`user_api_key` varchar(32) NOT NULL,
`user_auth_key` varchar(32) DEFAULT NULL,
`user_paypal_key` varchar(32) DEFAULT NULL,
`user_timezone_id` smallint(3) unsigned NOT NULL,
`user_group_id` tinyint(3) unsigned NOT NULL,
`user_custom_permission_mask_id` tinyint(3) unsigned DEFAULT NULL,
`user_lang_id` tinyint(2) unsigned NOT NULL,
`user_time_registered` int(10) unsigned NOT NULL,
`user_time_last_active` int(10) unsigned NOT NULL
PRIMARY KEY (`user_id`),
UNIQUE KEY `user_email` (`user_email`),
KEY `user_group_id` (`user_group_id`),
KEY `user_auth_key` (`user_auth_key`),
KEY `user_api_key` (`user_api_key`),
KEY `user_custom_permission_mask_id` (`user_custom_permission_mask_id`),
KEY `user_time_last_active` (`user_time_last_active`),
KEY `user_paypal_key` (`user_paypal_key`),
KEY `user_name` (`user_name`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=33 ;
-- --------------------------------------------------------
--
-- Table structure for table `user_groups`
--
CREATE TABLE IF NOT EXISTS `user_groups` (
`user_group_id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,
`user_group_name` varchar(32) NOT NULL,
`user_group_permission_mask_id` tinyint(3) unsigned NOT NULL,
`user_group_icon` varchar(32) DEFAULT NULL,
PRIMARY KEY (`user_group_id`),
KEY `user_group_permission_mask_id` (`user_group_permission_mask_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=8 ;
-- --------------------------------------------------------
--
-- Table structure for table `user_profile`
--
CREATE TABLE IF NOT EXISTS `user_profile` (
`user_id` mediumint(8) unsigned NOT NULL,
`user_signature_original` text,
`user_signature_html` text,
`user_avatar` varchar(64) DEFAULT NULL,
`user_steam_id` varchar(64) DEFAULT NULL,
`user_ps_id` varchar(16) DEFAULT NULL,
`user_xbox_id` varchar(64) DEFAULT NULL,
`user_wii_id` varchar(64) DEFAULT NULL,
PRIMARY KEY (`user_id`),
KEY `user_steam_id` (`user_steam_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
值得運行「優化」(http://dev.mysql.com/doc/refman/5.0/en/optimize-table.html) - 尤其是如果您的表格增長迅速。 – 2012-01-04 13:27:12
這仍然是在開發環境中,所以表格並不是很大。然而我試過了,它似乎有了很大的變化,現在正在使用索引並且運行得更快。 – robjbrain 2012-01-04 13:31:48
您是否願意提供有關優化程序的使用和實用性的更多信息,並定期在實時環境中運行它。如果你添加一個完整的答案,而不只是一個評論,我將能夠接受你的答案:) – robjbrain 2012-01-04 13:33:15