如何通过mysql中的连接来提高性能顺序

Question

我正在研究社交网络跟踪应用程序.即使连接正常索引也可以正常工作.但是当我添加order by子句时,总查询执行的时间要长100倍.以下查询用于获取没有order by子句的twitter_users.

SELECT DISTINCT  `tracked_twitter`.id
FROM tracked_twitter
INNER JOIN  `twitter_content` ON  `tracked_twitter`.`id` = `twitter_content`.`tracked_twitter_id` 
INNER JOIN  `tracker_twitter_content` ON  `twitter_content`.`id` = `tracker_twitter_content`.`twitter_content_id` 
AND  `tracker_twitter_content`.`tracker_id` =  '88'
LIMIT 20

显示0到19行(总计20行,查询占用0.0714秒)

但是当我添加order by子句时(在索引列上)

SELECT DISTINCT  `tracked_twitter`.id
FROM tracked_twitter
INNER JOIN  `twitter_content` ON  `tracked_twitter`.`id` =  `twitter_content`.`tracked_twitter_id` 
INNER JOIN  `tracker_twitter_content` ON  `twitter_content`.`id` =  `tracker_twitter_content`.`twitter_content_id` 
AND  `tracker_twitter_content`.`tracker_id` =  '88'
ORDER BY tracked_twitter.followers_count DESC 
LIMIT 20

显示0到19行(共计20行,查询占用13.4636秒)

说明

当我单独在其表中实现order by子句时,不需要花费太多时间

SELECT * FROM `tracked_twitter` WHERE 1 order by `followers_count` desc limit 20

显示行0 - 19(总共20行,查询占用0.0711秒)[followers_count:68236387 - 10525612]

表创建查询如下

CREATE TABLE IF NOT EXISTS `tracked_twitter` (
    `id` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
    `handle` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
    `name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
    `location` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
    `description` text COLLATE utf8_unicode_ci,
    `profile_image` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
    `followers_count` int(11) NOT NULL,
    `is_influencer` tinyint(1) NOT NULL DEFAULT '0',
    `created_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
    `updated_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
    `gender` enum('Male','Female','Other') COLLATE utf8_unicode_ci 
     DEFAULT NULL,
     PRIMARY KEY (`id`),
     KEY `followers_count` (`followers_count`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

因此,当我在其表上执行时,加入并不会减慢查询和顺序.那么我该如何提高性能呢？

更新1

@GordonLinoff方法解决了我是否只需要父表的结果集.我想知道每人的推文数量(与tracked_twitter表匹配的twitter_content计数).我怎么修改它？如果我想在推文内容上有数学函数我该怎么办？

SELECT  `tracked_twitter` . * , COUNT( * ) AS twitterContentCount, retweet_count + favourite_count + reply_count AS engagement
FROM  `tracked_twitter` 
INNER JOIN  `twitter_content` ON  `tracked_twitter`.`id` =  `twitter_content`.`tracked_twitter_id` 
INNER JOIN  `tracker_twitter_content` ON  `twitter_content`.`id` =  `tracker_twitter_content`.`twitter_content_id` 
WHERE  `is_influencer` !=  '1'
AND  `tracker_twitter_content`.`tracker_id` =  '88'
AND  `tracked_twitter_id` !=  '0'
GROUP BY  `tracked_twitter`.`id` 
ORDER BY twitterContentCount DESC 
LIMIT 20 
OFFSET 0

Answer 1

尝试摆脱distinct. 这是性能杀手。我不确定为什么你的第一个查询运行得很快；也许 MySQL 足够聪明，可以优化掉它。

我会尝试：

SELECT tt.id
FROM tracked_twitter tt
WHERE EXISTS (SELECT 1
              FROM twitter_content tc INNER JOIN  
                   tracker_twitter_content ttc
                   ON  tc.id =  ttc.twitter_content_id
              WHERE  ttc.tracker_id =  88 AND
                     tt.id =  tc.tracked_twitter_id
             )
ORDER BY tt.followers_count DESC ;

对于此版本，您需要以下索引： tracked_twitter(followers_count, id)、twitter_content(tracked_twitter_id, id)和 tracker_twitter_content(twitter_content_id, tracker_id)。