提高了許多LEFT一個SQL查詢的性能JOIN的

Question

我有一個數據庫結構與下面的協會服務了新聞報道：

• HABTM news_categories
• HABTM標籤
• HABTM上傳

我寫了一條SQL查詢將所有這一切拉到一起：

SELECT `news_articles`.*, 
GROUP_CONCAT(DISTINCT tags.title) AS `tags`, 
GROUP_CONCAT(DISTINCT tags.id) AS `tag_ids`, 
GROUP_CONCAT(DISTINCT news_categories.title) AS `news_categories`, 
GROUP_CONCAT(DISTINCT news_categories.id) AS `news_category_ids`, 
GROUP_CONCAT(DISTINCT news_categories.slug) AS `news_category_slugs`, 
`news_articles_uploads`.`caption` AS `upload_caption`, 
`uploads`.`title` AS `upload_title`, 
`uploads`.`basename` AS `upload_basename`, 
`uploads`.`extension` AS `upload_extension`, 
`uploads`.`path` AS `upload_path` 
FROM `news_articles` 
LEFT JOIN `news_articles_tags` ON news_articles_tags.news_article_id = news_articles.id 
LEFT JOIN `tags` ON news_articles_tags.tag_id = tags.id 
LEFT JOIN `news_articles_news_categories` ON news_articles_news_categories.news_article_id = news_articles.id 
LEFT JOIN `news_categories` ON news_articles_news_categories.news_category_id = news_categories.id 
LEFT JOIN `news_articles_uploads` ON (news_articles_uploads.news_article_id = news_articles.id AND news_articles_uploads.order = 0) 
LEFT JOIN `uploads` ON news_articles_uploads.upload_id = uploads.id 
WHERE (news_categories.slug IN ("category-one","category-two","category-three","category-four","category-five")) AND (news_articles.published = 1) 
GROUP BY `news_articles`.`id` 
ORDER BY `news_articles`.`lead_article` DESC, `news_articles`.`created` DESC LIMIT 20; 

問題是，在查詢運行時，速度很慢，而在繁忙時段，CPU使用率變得非常不可收拾！

下面是一個解釋上面的查詢（右鍵單擊在新標籤中打開看原圖）：

你可以在這裏找到的模式：http://pastie.org/private/qoe2qo16rbqr5mptb4bug

的服務器運行MySQL 5.1.55，網站使用Zend Framework來執行查詢和PHP 5.2.8。

我已經通過MySQL慢速查詢日誌，並添加了我所知道的最好的缺失索引，但查詢仍顯示爲需要1-3秒才能執行。如果有人有任何想法，我非常感激。提前致謝。

Answer 1

由於您的「WHERE」子句最初在您的新聞類別中包含「AND」的 指定的列表，因此強制INNER加入的連接不是LEFT JOIN。 另外，我會嘗試添加「STRAIGHT_JOIN」子句。這通常會強制引擎 以特別聲明的順序執行加入，而不是試圖爲您自己設想 替代方案......尤其是當其他表格更「查找」引用時。

我也會應用喬丹建議的指數。

SELECT STRAIGHT_JOIN 
     NA.*, 
     GROUP_CONCAT(DISTINCT tags.title) AS `tags`, 
     GROUP_CONCAT(DISTINCT tags.id) AS tag_ids, 
     GROUP_CONCAT(DISTINCT NC.title) AS news_categories, 
     GROUP_CONCAT(DISTINCT NC.id) AS news_category_ids, 
     GROUP_CONCAT(DISTINCT NC.slug) AS news_category_slugs, 
     NAUp.`caption` AS upload_caption, 
     Up1.`title` AS upload_title, 
     Up1.`basename` AS upload_basename, 
     Up1.`extension` AS upload_extension, 
     Up1.`path` AS upload_path 
    FROM 
     news_articles NA 
     INNER JOIN news_articles_news_categories NACats 
      ON NA.id = NACats.news_article_id 

      INNER JOIN news_categories NC 
       ON NACats.news_category_id = NC.id 
       AND NC.slug IN ("category-one", 
           "category-two", 
           "category-three", 
           "category-four", 
           "category-five") 


     LEFT JOIN news_articles_tags NATags 
      ON NA.ID = NATags.news_article_id 

      LEFT JOIN tags 
       ON NATags.tag_id = tags.id 

     LEFT JOIN news_articles_uploads NAUp 
      ON NA.ID = NAUp.news_article_id 
       AND NAUp.order = 0 

      LEFT JOIN uploads Up1 
       ON NAUp.upload_id = Up1.id 

    WHERE 
     NA.Published = 1 
    GROUP BY 
     NA.ID 
    ORDER BY 
     NA.lead_article DESC, 
     NA.created DESC 
    LIMIT 20; 

Answer 2

你有一個索引news_articles。 lead_article，news_articles。 created，這是一個包含兩列的索引。

create index news_articles_x1 on news_articles (lead_articles, created); 

沒有它，你將不會利用limit子句的順序，它仍然會掃描整個表並進行排序。

另外我會問你是否需要在一次爆炸中的所有這些數據？