Question

真的希望某种性能高手可以向我解释为什么单个连接导致查询速度变慢10倍。（另外，请不要大笑这个查询的大小！我想在我的数据库中输出整个目录以输出一个查询。我不确定将它分解为更小的查询是否会更快似乎不对。）

SELECT `c`.`categoryID`,
       `cl`.`name` AS `category_name`,
       `v`.*,
       TRUE AS `categoried`,
       GROUP_CONCAT(DISTINCT t_v.iso_3166_1_alpha_2) AS `video_territories`,
       GROUP_CONCAT(DISTINCT t_c.iso_3166_1_alpha_2) AS `category_territories`,
       `vl`.*,
       GROUP_CONCAT(DISTINCT kl.name) AS `keywords`
FROM `tblCategories` AS `c`
INNER JOIN `tblCategoryLocalisedData` AS `cl` ON c.categoryID = cl.categoryID
LEFT JOIN `tblCategoryDurations` AS `cd` ON c.categoryID = cd.categoryID
LEFT JOIN `tblCategoryRules` AS `cr` ON c.categoryID = cr.categoryID
LEFT JOIN `tblCategoryVideos` AS `cv` ON c.categoryID = cv.categoryID
LEFT JOIN `tblVideos` AS `v` ON cv.videoID = v.videoID
LEFT JOIN `tblVideoTerritories` AS `vt` ON vt.videoID = v.videoID
LEFT JOIN `tblCategoryTerritories` AS `ct` ON ct.categoryID = c.categoryID
INNER JOIN `tblTerritories` AS `t_v` ON t_v.territoryID = vt.territoryID
INNER JOIN `tblTerritories` AS `t_c` ON t_c.territoryID = ct.territoryID
INNER JOIN `tblVideoLocalisedData` AS `vl` ON vl.videoID = v.videoID
LEFT JOIN `tblVideoKeywords` AS `vk` ON v.videoID = vk.videoID
LEFT JOIN `tblKeywords` AS `k` ON vk.keywordID = k.keywordID
LEFT JOIN `tblKeywordLocalisedData` AS `kl` ON kl.keywordID = k.keywordID
INNER JOIN `tblLanguages` AS `l`
WHERE (cv.disabled IS NULL)
  AND (cd.start_date < NOW() OR cd.start_date IS NULL)
  AND (cd.end_date > NOW() OR cd.end_date IS NULL)
  AND (cr.name IS NULL)
  AND (l.languageID = cl.languageID OR cl.languageID IS NULL)
  AND (l.languageID = kl.languageID OR kl.languageID IS NULL)
  AND (l.languageID = vl.languageID OR vl.languageID IS NULL)
  AND (l.iso_639_1 = 'en')
GROUP BY `v`.`videoID`, `c`.`categoryID`
ORDER BY `c`.`categoryID` ASC

当我运行上述查询时，需要1秒钟才能完成。我试着在它上面运行一个EXPLAIN，它给了我这个：

+----+-------------+-------+--------+--------------------------------------------------------------------------------------+-----------------------------------------+---------+------------------------+------+----------------------------------------------+
| id | select_type | table | type   | possible_keys                                                                        | key                                     | key_len | ref                    | rows | Extra                                        |
+----+-------------+-------+--------+--------------------------------------------------------------------------------------+-----------------------------------------+---------+------------------------+------+----------------------------------------------+
|  1 | SIMPLE      | cv    | ALL    | fk_tblCategoryVideos_tblCategories1,fk_tblCategoryVideos_tblVideos1                  | NULL                                    | NULL    | NULL                   |    2 | Using where; Using temporary; Using filesort |
|  1 | SIMPLE      | c     | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.cv.categoryID  |    1 | Using index                                  |
|  1 | SIMPLE      | cd    | ref    | fk_tblCategoryDurations_tblCategories                                                | fk_tblCategoryDurations_tblCategories   | 4       | db.cv.categoryID  |    1 | Using where                                  |
|  1 | SIMPLE      | cr    | ref    | fk_tblCategoryRules_tblCategories1                                                   | fk_tblCategoryRules_tblCategories1      | 4       | db.cv.categoryID  |    1 | Using where; Not exists                      |
|  1 | SIMPLE      | vt    | ref    | fk_tblVideoTerritories_tblVideos1,fk_tblVideoTerritories_tblTerritories1             | fk_tblVideoTerritories_tblVideos1       | 4       | db.cv.videoID     |    1 | Using where                                  |
|  1 | SIMPLE      | t_v   | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.vt.territoryID |    1 |                                              |
|  1 | SIMPLE      | v     | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.vt.videoID     |    1 | Using where                                  |
|  1 | SIMPLE      | vk    | ref    | fk_tblVideoKeywords_tblVideos1                                                       | fk_tblVideoKeywords_tblVideos1          | 4       | db.cv.videoID     |    6 |                                              |
|  1 | SIMPLE      | k     | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.vk.keywordID   |    1 | Using index                                  |
|  1 | SIMPLE      | kl    | ref    | fk_tblKeywordLocalisedData_tblKeywords1                                              | fk_tblKeywordLocalisedData_tblKeywords1 | 4       | db.k.keywordID    |    1 |                                              |
|  1 | SIMPLE      | cl    | ALL    | fk_tblCategoryLocalisedData_tblCategories1,fk_tblCategoryLocalisedData_tblLanguages1 | NULL                                    | NULL    | NULL                   |    5 | Using where; Using join buffer               |
|  1 | SIMPLE      | l     | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.cl.languageID  |    1 | Using where                                  |
|  1 | SIMPLE      | ct    | ALL    | fk_tblCategoryTerritories_tblCategories1,fk_tblCategoryTerritories_tblTerritories1   | NULL                                    | NULL    | NULL                   |    2 | Using where; Using join buffer               |
|  1 | SIMPLE      | vl    | ALL    | fk_tblVideoLocalisedData_tblLanguages1,fk_tblVideoLocalisedData_tblVideos1           | NULL                                    | NULL    | NULL                   |    9 | Using where; Using join buffer               |
|  1 | SIMPLE      | t_c   | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.ct.territoryID |    1 |                                              |
+----+-------------+-------+--------+--------------------------------------------------------------------------------------+-----------------------------------------+---------+------------------------+------+----------------------------------------------+

但我不知道这意味着什么。我该如何解决这个问题？谢天谢地，我知道查询的哪些部分会导致大幅减速。如果我从tblVideoTerritories（vt）到tblTerritories（t_v）或tblCategoryTerritories（ct）到tblTerritories（t_c）删除连接，那么一切都会大大加快。我认为首先可能是因为GROUP_CONCAT或DISTINCT，但我尝试删除这些并且它几乎没有任何变化。似乎性能问题是由于加入同一个表'tblTerritories'两次引起的。如果我只有其中一个连接，则查询只需要0.1秒或0.2秒即可运行 - 这仍然是一段很长的时间，但这是一个更好的开始！

我想知道的是如何解决这个性能问题？ 为什么两次加入同一个表会导致查询花费10倍的时间？！

感谢您的帮助！

修改关于tblVideoTerritories的SHOW CREATE TABLE给了我：

CREATE TABLE `tblVideoTerritories` (
  `videoTerritoryID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `videoID` int(10) unsigned NOT NULL,
  `territoryID` int(10) unsigned NOT NULL,
  PRIMARY KEY (`videoTerritoryID`),
  KEY `fk_tblVideoTerritories_tblVideos1` (`videoID`),
  KEY `fk_tblVideoTerritories_tblTerritories1` (`territoryID`),
  CONSTRAINT `fk_tblVideoTerritories_tblTerritories1` FOREIGN KEY (`territoryID`) REFERENCES `tblTerritories` (`territoryID`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_tblVideoTerritories_tblVideos1` FOREIGN KEY (`videoID`) REFERENCES `tblVideos` (`videoID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

关于tblCategoryTerritories的SHOW CREATE TABLE给了我：

CREATE TABLE `tblCategoryTerritories` (
  `categoryTerritoryID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `categoryID` int(10) unsigned NOT NULL,
  `territoryID` int(10) unsigned NOT NULL,
  PRIMARY KEY (`categoryTerritoryID`),
  KEY `fk_tblCategoryTerritories_tblCategories1` (`categoryID`),
  KEY `fk_tblCategoryTerritories_tblTerritories1` (`territoryID`),
  CONSTRAINT `fk_tblCategoryTerritories_tblCategories1` FOREIGN KEY (`categoryID`) REFERENCES `tblCategories` (`categoryID`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_tblCategoryTerritories_tblTerritories1` FOREIGN KEY (`territoryID`) REFERENCES `tblTerritories` (`territoryID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

tblTerritories上的SHOW CREATE TABLE给了我：

CREATE TABLE `tblTerritories` (
  `territoryID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `iso_3166_1_alpha_2` char(2) COLLATE utf8_unicode_ci DEFAULT NULL,
  `iso_3166_1_alpha_3` char(3) COLLATE utf8_unicode_ci DEFAULT NULL,
  `defaultLanguageID` int(10) unsigned DEFAULT NULL,
  PRIMARY KEY (`territoryID`),
  KEY `fk_tblTerritories_tblLanguages1` (`defaultLanguageID`),
  KEY `iso_3166_1_alpha_2` (`iso_3166_1_alpha_2`),
  CONSTRAINT `fk_tblTerritories_tblLanguages1` FOREIGN KEY (`defaultLanguageID`) REFERENCES `tblLanguages` (`languageID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

EDIT2： 两次加入同一地区的原因是我需要使用查询顶部的GROUP_CONCAT生成两个单独的地区列表。我需要一个用于视频，一个用于它所属的类别。

EDIT3： 有趣的是，如果我将查询减少到它的裸骨，那么即使加入同一个表两次，它也非常快（0.00秒）：

    SELECT `c`.`categoryID`,
           `v`.`videoID`,
           GROUP_CONCAT(DISTINCT t_v.iso_3166_1_alpha_2) AS `video_territories`,
           GROUP_CONCAT(DISTINCT t_c.iso_3166_1_alpha_2) AS `category_territories`
FROM `tblCategories` AS `c`
LEFT JOIN `tblCategoryVideos` AS `cv` ON c.categoryID = cv.categoryID
LEFT JOIN `tblVideos` AS `v` ON cv.videoID = v.videoID
LEFT JOIN `tblVideoTerritories` AS `vt` ON vt.videoID = v.videoID
LEFT JOIN `tblCategoryTerritories` AS `ct` ON ct.categoryID = c.categoryID
INNER JOIN `tblTerritories` AS `t_v` ON t_v.territoryID = vt.territoryID
INNER JOIN `tblTerritories` AS `t_c` ON t_c.territoryID = ct.territoryID
GROUP BY `v`.`videoID`, `c`.`categoryID`

edit4： 如果我从使用WHERE作为临时搭建开启，那么我仍然有一个需要0.98秒的查询：

SELECT `c`.`categoryID`,
       `cl`.`name` AS `category_name`,
       `v`.*,
       TRUE AS `categoried`,
       GROUP_CONCAT(DISTINCT t_v.iso_3166_1_alpha_2) AS `video_territories`,
       GROUP_CONCAT(DISTINCT t_c.iso_3166_1_alpha_2) AS `category_territories`,
       `vl`.*,
       GROUP_CONCAT(DISTINCT kl.name) AS `keywords`
FROM `tblCategories` AS `c`
INNER JOIN `tblCategoryLocalisedData` AS `cl` ON c.categoryID = cl.categoryID
LEFT JOIN `tblCategoryDurations` AS `cd` ON c.categoryID = cd.categoryID
LEFT JOIN `tblCategoryRules` AS `cr` ON c.categoryID = cr.categoryID
LEFT JOIN `tblCategoryVideos` AS `cv` ON c.categoryID = cv.categoryID
LEFT JOIN `tblVideos` AS `v` ON cv.videoID = v.videoID
LEFT JOIN `tblVideoTerritories` AS `vt` ON vt.videoID = v.videoID
LEFT JOIN `tblCategoryTerritories` AS `ct` ON ct.categoryID = c.categoryID
INNER JOIN `tblTerritories` AS `t_v` ON t_v.territoryID = vt.territoryID
INNER JOIN `tblTerritories` AS `t_c` ON t_c.territoryID = ct.territoryID
INNER JOIN `tblVideoLocalisedData` AS `vl` ON vl.videoID = v.videoID
LEFT JOIN `tblVideoKeywords` AS `vk` ON v.videoID = vk.videoID
LEFT JOIN `tblKeywords` AS `k` ON vk.keywordID = k.keywordID
LEFT JOIN `tblKeywordLocalisedData` AS `kl` ON kl.keywordID = k.keywordID
INNER JOIN `tblLanguages` AS `l` ON (l.languageID = cl.languageID OR cl.languageID IS NULL) AND (l.languageID = kl.languageID OR kl.languageID IS NULL) AND (l.languageID = vl.languageID OR vl.languageID IS NULL)
WHERE (cv.disabled IS NULL)
  AND (cd.start_date < NOW() OR cd.start_date IS NULL)
  AND (cd.end_date > NOW() OR cd.end_date IS NULL)
  AND (cr.name IS NULL) AND (l.iso_639_1 = 'en')
GROUP BY `v`.`videoID`, `c`.`categoryID`
ORDER BY `c`.`categoryID` ASC

edit5： 如果我删除关键字相关联接，则查询在0.09秒内发生...删除tblKeyword和tblKeywordLocalisedData但是留下tblVideoKeywords给我0.80秒。删除tblVideoKeywords给我0.09秒。

但它似乎又有了索引，但我还没有得到它：

CREATE TABLE `tblVideoKeywords` (
  `videoKeywordID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `videoID` int(10) unsigned NOT NULL,
  `keywordID` int(10) unsigned NOT NULL,
  PRIMARY KEY (`videoKeywordID`),
  KEY `fk_tblVideoKeywords_tblVideos1` (`videoID`),
  KEY `fk_tblVideoKeywords_tblKeywords1` (`keywordID`),
  CONSTRAINT `fk_tblVideoKeywords_tblKeywords1` FOREIGN KEY (`keywordID`) REFERENCES `tblKeywords` (`keywordID`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_tblVideoKeywords_tblVideos1` FOREIGN KEY (`videoID`) REFERENCES `tblVideos` (`videoID`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=18 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

edit6： 使用DRapp提供的查询可以使一切更快。他的查询的解释现在给了我：

+----+-------------+---------+--------+--------------------------------------------------------------------------------------+-----------------------------------------+---------+------------------------+------+----------------------------------------------+
| id | select_type | table   | type   | possible_keys                                                                        | key                                     | key_len | ref                    | rows | Extra                                        |
+----+-------------+---------+--------+--------------------------------------------------------------------------------------+-----------------------------------------+---------+------------------------+------+----------------------------------------------+
|  1 | SIMPLE      | c       | index  | PRIMARY                                                                              | PRIMARY                                 | 4       | NULL                   |    3 | Using index; Using temporary; Using filesort |
|  1 | SIMPLE      | cl      | ALL    | fk_tblCategoryLocalisedData_tblCategories1,fk_tblCategoryLocalisedData_tblLanguages1 | NULL                                    | NULL    | NULL                   |    5 | Using where; Using join buffer               |
|  1 | SIMPLE      | lang_cl | ALL    | PRIMARY                                                                              | NULL                                    | NULL    | NULL                   |    2 | Using where; Using join buffer               |
|  1 | SIMPLE      | cd      | ref    | fk_tblCategoryDurations_tblCategories                                                | fk_tblCategoryDurations_tblCategories   | 4       | db.c.categoryID   |    1 |                                              |
|  1 | SIMPLE      | cr      | ref    | fk_tblCategoryRules_tblCategories1                                                   | fk_tblCategoryRules_tblCategories1      | 4       | db.c.categoryID   |    1 | Using where; Not exists                      |
|  1 | SIMPLE      | cv      | ALL    | fk_tblCategoryVideos_tblCategories1,fk_tblCategoryVideos_tblVideos1                  | NULL                                    | NULL    | NULL                   |    2 | Using where; Using join buffer               |
|  1 | SIMPLE      | ct      | ALL    | fk_tblCategoryTerritories_tblCategories1,fk_tblCategoryTerritories_tblTerritories1   | NULL                                    | NULL    | NULL                   |    2 | Using where; Using join buffer               |
|  1 | SIMPLE      | t_c     | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.ct.territoryID |    1 |                                              |
|  1 | SIMPLE      | v       | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.cv.videoID     |    1 | Using where                                  |
|  1 | SIMPLE      | vt      | ref    | fk_tblVideoTerritories_tblVideos1,fk_tblVideoTerritories_tblTerritories1             | fk_tblVideoTerritories_tblVideos1       | 4       | db.v.videoID      |    1 | Using where                                  |
|  1 | SIMPLE      | t_v     | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.vt.territoryID |    1 |                                              |
|  1 | SIMPLE      | vl      | ALL    | fk_tblVideoLocalisedData_tblLanguages1,fk_tblVideoLocalisedData_tblVideos1           | NULL                                    | NULL    | NULL                   |    9 | Using where; Using join buffer               |
|  1 | SIMPLE      | lang_vl | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.vl.languageID  |    1 | Using where                                  |
|  1 | SIMPLE      | vk      | ALL    | fk_tblVideoKeywords_tblVideos1,fk_tblVideoKeywords_tblKeywords1                      | NULL                                    | NULL    | NULL                   |   15 | Using where; Using join buffer               |
|  1 | SIMPLE      | k       | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.vk.keywordID   |    1 | Using where; Using index                     |
|  1 | SIMPLE      | kl      | ref    | fk_tblKeywordLocalisedData_tblKeywords1,fk_tblKeywordLocalisedData_tblLanguages1     | fk_tblKeywordLocalisedData_tblKeywords1 | 4       | db.k.keywordID    |    1 | Using where                                  |
|  1 | SIMPLE      | lang_kl | eq_ref | PRIMARY                                                                              | PRIMARY                                 | 4       | db.kl.languageID  |    1 | Using where                                  |
+----+-------------+---------+--------+--------------------------------------------------------------------------------------+-----------------------------------------+---------+------------------------+------+----------------------------------------------+
17 rows in set (0.01 sec)

Answer 1

除了其他几个问题，我也回答过类似的问题，只需添加一个“STRAIGHT_JOIN”，轻微的重组就可以提供帮助。查询优化器实际上会尝试针对所有表进行思考，尝试查找记录较少的表并将其连接到较大的表，从而导致总混乱。这种情况发生在我通过查询超过14个子表时查看1400多万条记录的数据...非常类似于你在这里发生的事情。在专用的独立服务器上运行了30多个小时的查询并将其挂起，不到2小时......请尝试以下操作：

除了对我习惯的连接进行一些视觉清理/排序之外，我还采用了一些NOW（）和NULL并将它们移动到连接中。如果查询左连接并将日期作为连接限定符的一部分，则将排除那些超出范围的记录，从而保留NULL结果集或有效条目，不需要将该限定符加倍。

SELECT STRAIGHT_JOIN
      c.categoryID,
      cl.name AS category_name,
      v.*,
      TRUE AS categoried,
      GROUP_CONCAT(DISTINCT t_v.iso_3166_1_alpha_2) AS video_territories,
      GROUP_CONCAT(DISTINCT t_c.iso_3166_1_alpha_2) AS category_territories,
      vl.*,
      GROUP_CONCAT(DISTINCT kl.name) AS keywords
   FROM 
      tblCategories AS c
         INNER JOIN tblCategoryLocalisedData AS cl
            ON c.categoryID = cl.categoryID 
            INNER JOIN tblLanguages AS lang_cl
               ON l.languageID = lang_cl.languageID
                  AND lang_cl.iso_639_1 = 'en'
         LEFT JOIN tblCategoryDurations AS cd
            ON c.categoryID = cd.categoryID 
              AND cd.start_date < NOW()
              AND cd.end_date > NOW()
         LEFT JOIN tblCategoryRules AS cr
            ON c.categoryID = cr.categoryID 
         LEFT JOIN tblCategoryVideos AS cv
            ON c.categoryID = cv.categoryID 
         LEFT JOIN tblCategoryTerritories AS ct
            ON c.categoryID = ct.categoryID
            INNER JOIN tblTerritories AS t_c 
               ON ct.territoryID = t_c.territoryID
         LEFT JOIN tblVideos AS v
            ON cv.videoID = v.videoID 
            LEFT JOIN tblVideoTerritories AS vt
               ON v.videoID = vt.videoID
               INNER JOIN tblTerritories AS t_v
                  ON vt.territoryID = t_v.territoryID
            INNER JOIN tblVideoLocalisedData AS vl
               ON v.videoID = vl.videoID
               INNER JOIN tblLanguages AS lang_vl
                   ON vl.languageID = lang_vl.languageID
                      AND lang_vl.iso_639_1 = 'en'
            LEFT JOIN tblVideoKeywords AS vk
               ON v.videoID = vk.videoID 
               LEFT JOIN tblKeywords AS k
                  ON vk.keywordID = k.keywordID 
                  LEFT JOIN tblKeywordLocalisedData AS kl
                     ON k.keywordID = kl.keywordID
                     INNER JOIN tblLanguages AS lang_kl
                        ON kl.languageID = lang_kl.languageID
                          AND lang_kl.iso_639_1 = 'en'
   WHERE 
          (  cv.disabled IS NULL)   
      AND (  cr.name IS NULL)   
   GROUP BY 
      v.videoID, 
      c.categoryID
   ORDER BY 
      c.categoryID ASC

如上所述，STRAIGHT_JOIN基本上告诉优化器“不要为我考虑”....按照我告诉你的顺序进行查询。在这种情况下，使用“tblCategories”作为主表并链接其他所有内容。优化器，即使有解释可能会尝试慢，并在下次运行查询时尝试不同的方法。因此，它可以尝试首先使用Languages表，然后通过其他表进行反向划分并阻塞。此外，通过将“AND”部分（例如日期）指向那些左连接，这些连接简化了WHERE，如您所见......正如您在NULL或它存在的位置，只是应用于该特定连接。保持干净的地方。

此外，通过保持关系的直接和缩进分别与他们加入的内容相关，更容易理解与哪些内容相关联...

我还想看看最后的“EXPLAIN”并看看它是什么。

慢SQL查询：在两个不同的连接中使用相同的表会导致查询速度变慢10倍！

1 个答案: