关于复杂的sql语句的建议

如何解决关于复杂的sql语句的建议

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SELECT `v`.*,GROUP_CONCAT(DISTINCT(`gg`.genre_id)) AS `genre_ids`,GROUP_CONCAT(DISTINCT(`gg`.genre_ru)) AS `genres`,GROUP_CONCAT(DISTINCT(`tg`.tag_id)) AS `tags_ids`,GROUP_CONCAT(DISTINCT(`tg`.name)) AS `tags`
FROM `video` AS `v`
LEFT JOIN `video_categories` AS `gc` ON gc.video_id = v.video_id
LEFT JOIN `video_genres` AS `gg` ON gg.genre_id = gc.genre_id
LEFT JOIN `tags_relations` AS `tr` ON tr.department=18 AND tr.parent_id = v.video_id
LEFT JOIN `tags` AS `tg` ON tg.tag_id = tr.tag_id
WHERE (v.video_id IN (
  SELECT gc2.video_id
  FROM video_categories gc2
  WHERE gc2.genre_id IN(44)
  GROUP BY gc2.video_id
  HAVING COUNT(gc2.video_id)=1)) 
AND (v.video_id IN (
  SELECT gc2.parent_id
  FROM tags_relations gc2
  WHERE gc2.tag_id IN(14) AND gc2.department=18
  GROUP BY gc2.parent_id
  HAVING COUNT(gc2.parent_id)=1))
GROUP BY `v`.`video_id`
ORDER BY `v`.`video_id` DESC

查询需要0.4s〜才能运行。这是因为WHERE语句中的子查询：

v.video_id IN (
    SELECT gc2.parent_id
    FROM tags_relations gc2
    WHERE gc2.tag_id IN(14) AND gc2.department=18
    GROUP BY gc2.parent_id
    HAVING COUNT(gc2.parent_id)=1
)

没有它，它会运行0.07s〜 也许尝试使用高级联接？害羞 谢谢 ;）     

解决方法

        在MySQL中，永远不要使用ѭ2，这是非常缓慢的。 改用联接：

SELECT `v`.*,GROUP_CONCAT(DISTINCT(`gg`.genre_id)) AS `genre_ids`,GROUP_CONCAT(DISTINCT(`gg`.genre_ru)) AS `genres`,GROUP_CONCAT(DISTINCT(`tg`.tag_id)) AS `tags_ids`,GROUP_CONCAT(DISTINCT(`tg`.name)) AS `tags`
FROM video AS v
INNER JOIN video_categories AS gc ON gc.video_id = v.video_id 
  AND gc2.genre_id = \'44\'
LEFT JOIN video_genres AS gg ON gg.genre_id = gc.genre_id
LEFT JOIN tags_relations AS tr ON tr.department=18 AND tr.parent_id = v.video_id
LEFT JOIN tags AS tg ON tg.tag_id = tr.tag_id
INNER JOIN tags_relations tr2 ON (tr2.parent_id = v.video_id 
  AND tr2.tag_id = 14 AND tr2.department=18
GROUP BY `v`.`video_id`
ORDER BY `v`.`video_id` DESC

    ,        

SELECT `v`.*,GROUP_CONCAT(DISTINCT(`tg`.name)) AS `tags`
FROM `video` AS `v`
LEFT JOIN `video_categories` AS `gc` ON gc.video_id = v.video_id
LEFT JOIN `video_genres` AS `gg` ON gg.genre_id = gc.genre_id
LEFT JOIN `tags_relations` AS `tr` ON tr.department=18 AND tr.parent_id = v.video_id
LEFT JOIN `tags` AS `tg` ON tg.tag_id = tr.tag_id
JOIN (
  SELECT gc2.video_id
  FROM video_categories gc2
  WHERE gc2.genre_id IN(44)
  GROUP BY gc2.video_id
  HAVING COUNT(gc2.video_id)=1
  ) vc ON v.video_id = vc.video_id
JOIN (
  SELECT gc2.parent_id
  FROM tags_relations gc2
  WHERE gc2.tag_id IN(14) AND gc2.department=18
  GROUP BY gc2.parent_id
  HAVING COUNT(gc2.parent_id)=1
  ) tr ON v.video_id = tr.parent_id
GROUP BY `v`.`video_id`
ORDER BY `v`.`video_id` DESC

编辑： 我仔细查看了您的查询，认为可以将其简化为以下内容：

SELECT `v1`.*,GROUP_CONCAT(DISTINCT(`tg`.name)) AS `tags`
FROM (
SELECT v.*
FROM `video` AS `v`
LEFT JOIN `video_categories` AS `gc` ON gc.video_id = v.video_id
LEFT JOIN `tags_relations` AS `tr` ON tr.parent_id = v.video_id
WHERE gc.genre_id IN(44)
  AND tr.tag_id IN(14)
  AND tr.department=18
GROUP BY `v`.`video_id`
HAVING COUNT(*) = 1
) v1
LEFT JOIN `video_genres` AS `gg` ON gg.genre_id = gc.genre_id
LEFT JOIN `tags` AS `tg` ON tg.tag_id = tr.tag_id
GROUP BY v1.video_id
ORDER BY v1.video_id DESC