如何通过 mysql 中的联接按性能提高顺序

Question

我正在开发社交网络跟踪应用程序。即使加入适当的索引也能正常工作。但是当我添加 order by 子句时，总查询需要 100 倍的时间来执行。下面的查询我曾经在没有 order by 子句的情况下获取 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

显示第 0 - 19 行（共 20 行，查询耗时 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

显示第 0 - 19 行（共 20 行，查询耗时 13.4636 秒）

解释

当我单独在 table 中实现 order by 子句时，它不会花费太多时间

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

显示第 0 - 19 行（总共 20 行，查询耗时 0.0711 秒）[followers_count：68236387 - 10525612]

table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;

所以当我在它的 table 上执行它时，join 运行良好，并没有减慢查询和顺序。那么如何提高性能呢？

更新 1

@GordonLinoff 方法解决了如果我只需要父 table 的结果集。我想知道每个人的推文数量（与 tracked_twitter table 匹配的 twitter_content 的计数）。我该如何修改它？如果我想在推文内容上使用数学函数，我该怎么做？？

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。那是一个性能杀手。我不确定为什么您的第一个查询运行得很快；也许 MySQL 足够聪明，可以优化它。

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，您需要索引：tracked_twitter(followers_count, id)、twitter_content(tracked_twitter_id, id) 和 tracker_twitter_content(twitter_content_id, tracker_id).

Answer 2

父级 table 保持在括号内

SELECT DISTINCT  `tracked_twitter`.id FROM
(SELECT id,followers_count  FROM tracked_twitter ORDER BY followers_count DESC 
LIMIT 20) AS 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

Answer 3

主要问题是，即使您的行数相对较少，您也使用 varchar(255) COLLATE utf8_unicode_ci 作为主键（而不是整数），因此作为其他表中的外键。我怀疑 twitter_content.id 也有同样的问题。这会导致大量长字符串比较并为临时表保留大量额外内存。

关于查询本身，是的，它应该是一个遍历 followers_count 索引并检查相关表的条件的查询。这可以按照 Gordon Linoff 的建议或使用索引提示来完成。

如何通过 mysql 中的联接按性能提高顺序

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