如何通過在mysql中加入表現來改善訂單

Question

我正在開發一個社交網絡跟蹤應用程序。即使連接適當的索引工作正常。但是，當我添加order by子句時，總查詢需要100倍的時間來執行。以下查詢我用於獲取twitter_users而不使用order by子句。

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 

顯示行0 - 19（20總計，查詢花費0.0714秒）

但是，當我通過子句添加順序（在索引列）

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 

顯示行0 - 19（ 20總計，查詢花費13.4636秒）

EXPLAIN

當我在它的單獨表子句執行的命令其不花費太多時間

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

顯示行0 - 19（20總計，查詢花費0.0711秒）[FOLLOWERS_COUNT：68236387 - 10525612]

該表的創建語句如下

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，加入由工作良好，當我執行它在其表沒有減速的查詢和訂單。那麼我該如何提高性能？

UPDATE 1

@GordonLinoff方法解決，如果我只需要結果從父表中設置。我想知道每個人的推文數（與tracked_twitter表匹配的twitter_content的計數）。我如何修改它？如果我想在推特內容上使用數學函數，我該怎麼做？

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

試着擺脫distinct。這是一個性能殺手。我不確定爲什麼您的第一個查詢很快就會生效;也許MySQL很聰明，可以優化它。

我會嘗試：

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 ; 

對於此版本，您想對指數：tracked_twitter(followers_count, id)，twitter_content(tracked_twitter_id, id)和 tracker_twitter_content(twitter_content_id, tracker_id)。

Answer 2

父表保持在支架與限制

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

的主要問題是，即使你有相對較少的行，你用varchar(255) COLLATE utf8_unicode_ci作爲主鍵（而不是整數），因此作爲外鍵其他表格。我懷疑同樣的問題是twitter_content.id。這會導致很多長字符串比較，併爲臨時表保留大量額外的內存。

關於查詢本身，是的，它應該是一個查詢，沿着followers_count索引走，並檢查相關表的條件。這可以按Gordon Linoff的建議完成，或者使用索引提示。